Filesystem(3)

NAME
Tcl_FSRegister, Tcl_FSUnregister, Tcl_FSData, Tcl_FSMountsChanged, Tcl_FSGetFileSystemForPath, Tcl_FSGetPathType, Tcl_FSCopyFile, Tcl_FSCopyDirectory, Tcl_FSCreateDirectory, Tcl_FSDeleteFile, Tcl_FSRemoveDirectory, Tcl_FSRenameFile, Tcl_FSListVolumes, Tcl_FSEvalFile, Tcl_FSLoadFile, Tcl_FSMatchInDirectory, Tcl_FSLink, Tcl_FSLstat, Tcl_FSUtime, Tcl_FSFileAttrsGet, Tcl_FSFileAttrsSet, Tcl_FSFileAttrStrings, Tcl_FSStat, Tcl_FSAccess, Tcl_FSOpenFileChannel, Tcl_FSGetCwd, Tcl_FSChdir, Tcl_FSPathSeparator, Tcl_FSJoinPath, Tcl_FSSplitPath, Tcl_FSEqualPaths, Tcl_FSGetNormalizedPath, Tcl_FSJoinToPath, Tcl_FSConvertToPathType, Tcl_FSGetInternalRep, Tcl_FSGetTranslatedPath, Tcl_FSGetTranslatedStringPath, Tcl_FSNewNativePath, Tcl_FSGetNativePath, Tcl_FSFileSystemInfo, Tcl_AllocStatBuf - procedures to interact with any filesystem

SYNOPSIS
#include <tcl.h>

int
Tcl_FSRegister(clientData, fsPtr)

int
Tcl_FSUnregister(fsPtr)

ClientData
Tcl_FSData(fsPtr)

void
Tcl_FSMountsChanged(fsPtr)

Tcl_Filesystem*
Tcl_FSGetFileSystemForPath(pathObjPtr)

Tcl_PathType
Tcl_FSGetPathType(pathObjPtr)

int
Tcl_FSCopyFile(srcPathPtr, destPathPtr)

int
Tcl_FSCopyDirectory(srcPathPtr, destPathPtr, errorPtr)

int
Tcl_FSCreateDirectory(pathPtr)

int
Tcl_FSDeleteFile(pathPtr)

int
Tcl_FSRemoveDirectory(pathPtr, int recursive, errorPtr)

int
Tcl_FSRenameFile(srcPathPtr, destPathPtr)

Tcl_Obj*
Tcl_FSListVolumes(void)

int
Tcl_FSEvalFile(interp, pathPtr)

int
Tcl_FSLoadFile(interp, pathPtr, sym1, sym2, proc1Ptr, proc2Ptr, handlePtr, unloadProcPtr)

int
Tcl_FSMatchInDirectory(interp, result, pathPtr, pattern, types)

Tcl_Obj*
Tcl_FSLink(linkNamePtr, toPtr, linkAction)

int
Tcl_FSLstat(pathPtr, statPtr)

int
Tcl_FSUtime(pathPtr, tval)

int
Tcl_FSFileAttrsGet(interp, int index, pathPtr, objPtrRef)

int
Tcl_FSFileAttrsSet(interp, int index, pathPtr, Tcl_Obj *objPtr)

CONST char**
Tcl_FSFileAttrStrings(pathPtr, objPtrRef)

int
Tcl_FSStat(pathPtr, statPtr)

int
Tcl_FSAccess(pathPtr, mode)

Tcl_Channel
Tcl_FSOpenFileChannel(interp, pathPtr, modeString, permissions)

Tcl_Obj*
Tcl_FSGetCwd(interp)

int
Tcl_FSChdir(pathPtr)

Tcl_Obj*
Tcl_FSPathSeparator(pathPtr)

Tcl_Obj*
Tcl_FSJoinPath(listObj, elements)

Tcl_Obj*
Tcl_FSSplitPath(pathPtr, lenPtr)

int
Tcl_FSEqualPaths(firstPtr, secondPtr)

Tcl_Obj*
Tcl_FSGetNormalizedPath(interp, pathPtr)

Tcl_Obj*
Tcl_FSJoinToPath(basePtr, objc, objv)

int
Tcl_FSConvertToPathType(interp, pathPtr)

ClientData
Tcl_FSGetInternalRep(pathPtr, fsPtr)

Tcl_Obj*
Tcl_FSGetTranslatedPath(interp, pathPtr)

CONST char*
Tcl_FSGetTranslatedStringPath(interp, pathPtr)

Tcl_Obj*
Tcl_FSNewNativePath(fsPtr, clientData)

CONST char*
Tcl_FSGetNativePath(pathPtr)

Tcl_Obj*
Tcl_FSFileSystemInfo(pathPtr)

Tcl_StatBuf*
Tcl_AllocStatBuf()

ARGUMENTS
Points to a structure containing the addresses of procedures that can be called to perform the various filesystem operations. The path represented by this object is used for the operation in question. If the object does not already have an internal path representation, it will be converted to have one. As for pathPtr, but used for the source file for a copy or rename operation. As for pathPtr, but used for the destination filename for a copy or rename operation. Only files or directories matching this pattern will be returned by Tcl_FSMatchInDirectory. Only files or directories matching the type descriptions contained in this structure will be returned by Tcl_FSMatchInDirectory. It is very important that the 'directory' flag is properly handled. This parameter may be NULL. Interpreter to use either for results, evaluation, or reporting error messages. The native description of the path object to create. The first of two path objects to compare. The object may be converted to path type. The second of two path objects to compare. The object may be converted to path type. The list of path elements to operate on with a join operation. If non-negative, the number of elements in the listObj which should be joined together. If negative, then all elements are joined. In the case of an error, filled with an object containing the name of the file which caused an error in the various copy/rename operations. Filled with an object containing the result of the operation. Pre-allocated object in which to store (by lappending) the list of files or directories which are successfully matched in Tcl_FSMatchInDirectory. Mask consisting of one or more of R_OK, W_OK, X_OK and F_OK. R_OK, W_OK and X_OK request checking whether the file exists and has read, write and execute permissions, respectively. F_OK just requests checking for the existence of the file. The structure that contains the result of a stat or lstat operation. Name of a procedure to look up in the file's symbol table Name of a procedure to look up in the file's symbol table Filled with the init function for this code. Filled with the safe-init function for this code. Filled with the clientData value to pass to this code's unload function when it is called. Filled with the function to use to unload this piece of code. The access and modification times in this structure are read and used to set those values for a given file. Specifies how the file is to be accessed. May have any of the values allowed for the mode argument to the Tcl open command. POSIX-style permission flags such as 0644. If a new file is created, these permissions will be set on the created file. If non-NULL, filled with the number of elements in the split path. The base path on to which to join the given elements. May be NULL. The number of elements in objv. The elements to join to the given base path.

DESCRIPTION

There are several reasons for calling the Tcl_FS... functions rather than calling system level functions like access and stat directly. First, they will work cross-platform, so an extension which calls them should work unmodified on Unix, MacOS and Windows. Second, the Windows implementation of some of these functions fixes some bugs in the system level calls. Third, these function calls deal with any 'Utf to platform-native' path conversions which may be required (and may cache the results of such conversions for greater efficiency on subsequent calls). Fourth, and perhaps most importantly, all of these functions are 'virtual filesystem aware'. Any virtual filesystem which has been registered (through Tcl_FSRegister) may reroute file access to alternative media or access methods. This means that all of these functions (and therefore the corresponding file, glob, pwd, cd, open, etc. Tcl commands) may be operate on 'files' which are not native files in the native filesystem. This also means that any Tcl extension which accesses the filesystem through this API is automatically 'virtual filesystem aware'. Of course, if an extension accesses the native filesystem directly (through platform-specific APIs, for example), then Tcl cannot intercept such calls.

If appropriate vfs's have been registered, the 'files' may, to give two examples, be remote (e.g. situated on a remote ftp server) or archived (e.g. lying inside a .zip archive). Such registered filesystems provide a lookup table of functions to implement all or some of the functionality listed here. Finally, the Tcl_FSStat and Tcl_FSLstat calls abstract away from what the 'struct stat' buffer buffer is actually declared to be, allowing the same code to be used both on systems with and systems without support for files larger than 2GB in size.

The Tcl_FS... are objectified and may cache internal representations and other path-related strings (e.g. the current working directory). One side-effect of this is that one must not pass in objects with a refCount of zero to any of these functions. If such calls were handled, they might result in memory leaks (under some circumstances, the filesystem code may wish to retain a reference to the passed in object, and so one must not assume that after any of these calls return, the object still has a refCount of zero - it may have been incremented), or in a direct segfault due to the object being freed part way through the complex object manipulation required to ensure that the path is fully normalized and absolute for filesystem determination. The practical lesson to learn from this is that Tcl_Obj *path = Tcl_NewStringObj(...) ; Tcl_FS...(path) ; Tcl_DecrRefCount(path) is wrong, and may segfault. The 'path' must have its refCount incremented before passing it in, or decrementing it. For this reason, objects with a refCount of zero are considered not to be valid filesystem paths and calling any Tcl_FS API with such an object will result in no action being taken.

Tcl_FSCopyFile attempts to copy the file given by srcPathPtr to the path name given by destPathPtr. If the two paths given lie in the same filesystem (according to Tcl_FSGetFileSystemForPath) then that filesystem's 'copy file' function is called (if it is non-NULL). Otherwise the function returns -1 and sets Tcl's errno to the 'EXDEV' posix error code (which signifies a 'cross-domain link').

Tcl_FSCopyDirectory attempts to copy the directory given by srcPathPtr to the path name given by destPathPtr. If the two paths given lie in the same filesystem (according to Tcl_FSGetFileSystemForPath) then that filesystem's 'copy file' function is called (if it is non-NULL). Otherwise the function returns -1 and sets Tcl's errno to the 'EXDEV' posix error code (which signifies a 'cross-domain link').

Tcl_FSCreateDirectory attempts to create the directory given by pathPtr by calling the owning filesystem's 'create directory' function.

Tcl_FSDeleteFile attempts to delete the file given by pathPtr by calling the owning filesystem's 'delete file' function.

Tcl_FSRemoveDirectory attempts to remove the directory given by pathPtr by calling the owning filesystem's 'remove directory' function.

Tcl_FSRenameFile attempts to rename the file or directory given by srcPathPtr to the path name given by destPathPtr. If the two paths given lie in the same filesystem (according to Tcl_FSGetFileSystemForPath) then that filesystem's 'rename file' function is called (if it is non-NULL). Otherwise the function returns -1 and sets Tcl's errno to the 'EXDEV' posix error code (which signifies a ``cross-domain link'').

Tcl_FSListVolumes calls each filesystem which has a non-NULL 'list volumes' function and asks them to return their list of root volumes. It accumulates the return values in a list which is returned to the caller (with a refCount of 0).

Tcl_FSEvalFile reads the file given by pathPtr and evaluates its contents as a Tcl script. It returns the same information as Tcl_EvalObjEx. If the file couldn't be read then a Tcl error is returned to describe why the file couldn't be read. The eofchar for files is '\32' (^Z) for all platforms. If you require a ``^Z'' in code for string comparison, you can use ``\032'' or ``\u001a'', which will be safely substituted by the Tcl interpreter into ``^Z''.

Tcl_FSLoadFile dynamically loads a binary code file into memory and returns the addresses of two procedures within that file, if they are defined. The appropriate function for the filesystem to which pathPtr belongs will be called. If that filesystem does not implement this function (most virtual filesystems will not, because of OS limitations in dynamically loading binary code), Tcl will attempt to copy the file to a temporary directory and load that temporary file.

Returns a standard Tcl completion code. If an error occurs, an error message is left in the interp's result.

Tcl_FSMatchInDirectory is used by the globbing code to search a directory for all files which match a given pattern. The appropriate function for the filesystem to which pathPtr belongs will be called.

The return value is a standard Tcl result indicating whether an error occurred in globbing. Error messages are placed in interp, but good results are placed in the resultPtr given.

Note that the 'glob' code implements recursive patterns internally, so this function will only ever be passed simple patterns, which can be matched using the logic of 'string match'. To handle recursion, Tcl will call this function frequently asking only for directories to be returned.

Tcl_FSLink replaces the library version of readlink(), and extends it to support the creation of links. The appropriate function for the filesystem to which linkNamePtr belongs will be called.

If the toPtr is NULL, a readlink action is performed. The result is a Tcl_Obj specifying the contents of the symbolic link given by linkNamePtr, or NULL if the link could not be read. The result is owned by the caller, which should call Tcl_DecrRefCount when the result is no longer needed. If the toPtr is not NULL, Tcl should create a link of one of the types passed in in the linkAction flag. This flag is an or'd combination of TCL_CREATE_SYMBOLIC_LINK and TCL_CREATE_HARD_LINK. Where a choice exists (i.e. more than one flag is passed in), the Tcl convention is to prefer symbolic links. When a link is successfully created, the return value should be toPtr (which is therefore already owned by the caller). If unsuccessful, NULL should be returned.

Tcl_FSLstat fills the stat structure statPtr with information about the specified file. You do not need any access rights to the file to get this information but you need search rights to all directories named in the path leading to the file. The stat structure includes info regarding device, inode (always 0 on Windows), privilege mode, nlink (always 1 on Windows), user id (always 0 on Windows), group id (always 0 on Windows), rdev (same as device on Windows), size, last access time, last modification time, and creation time.

If path exists, Tcl_FSLstat returns 0 and the stat structure is filled with data. Otherwise, -1 is returned, and no stat info is given.

Tcl_FSUtime replaces the library version of utime.

For results see 'utime' documentation. If successful, the function will update the 'atime' and 'mtime' values of the file given.

Tcl_FSFileAttrsGet implements read access for the hookable 'file attributes' subcommand. The appropriate function for the filesystem to which pathPtr belongs will be called.

If the result is TCL_OK, then an object was placed in objPtrRef, which will only be temporarily valid (unless Tcl_IncrRefCount is called).

Tcl_FSFileAttrsSet implements write access for the hookable 'file attributes' subcommand. The appropriate function for the filesystem to which pathPtr belongs will be called.

Tcl_FSFileAttrStrings implements part of the hookable 'file attributes' subcommand. The appropriate function for the filesystem to which pathPtr belongs will be called.

The called procedure may either return an array of strings, or may instead return NULL and place a Tcl list into the given objPtrRef. Tcl will take that list and first increment its refCount before using it. On completion of that use, Tcl will decrement its refCount. Hence if the list should be disposed of by Tcl when done, it should have a refCount of zero, and if the list should not be disposed of, the filesystem should ensure it retains a refCount on the object.

Tcl_FSAccess checks whether the process would be allowed to read, write or test for existence of the file (or other file system object) whose name is pathname. If pathname is a symbolic link on Unix, then permissions of the file referred by this symbolic link are tested.

On success (all requested permissions granted), zero is returned. On error (at least one bit in mode asked for a permission that is denied, or some other error occurred), -1 is returned.

Tcl_FSStat fills the stat structure statPtr with information about the specified file. You do not need any access rights to the file to get this information but you need search rights to all directories named in the path leading to the file. The stat structure includes info regarding device, inode (always 0 on Windows), privilege mode, nlink (always 1 on Windows), user id (always 0 on Windows), group id (always 0 on Windows), rdev (same as device on Windows), size, last access time, last modification time, and creation time.

If path exists, Tcl_FSStat returns 0 and the stat structure is filled with data. Otherwise, -1 is returned, and no stat info is given.

Tcl_FSOpenFileChannel opens a file specified by pathPtr and returns a channel handle that can be used to perform input and output on the file. This API is modeled after the fopen procedure of the Unix standard I/O library. The syntax and meaning of all arguments is similar to those given in the Tcl open command when opening a file. If an error occurs while opening the channel, Tcl_FSOpenFileChannel returns NULL and records a POSIX error code that can be retrieved with Tcl_GetErrno. In addition, if interp is non-NULL, Tcl_FSOpenFileChannel leaves an error message in interp's result after any error.

The newly created channel is not registered in the supplied interpreter; to register it, use Tcl_RegisterChannel, described below. If one of the standard channels, stdin, stdout or stderr was previously closed, the act of creating the new channel also assigns it as a replacement for the standard channel.

Tcl_FSGetCwd replaces the library version of getcwd().

It returns the Tcl library's current working directory. This may be different to the native platform's working directory, in the case for which the cwd is not in the native filesystem.

The result is a pointer to a Tcl_Obj specifying the current directory, or NULL if the current directory could not be determined. If NULL is returned, an error message is left in the interp's result.

The result already has its refCount incremented for the caller. When it is no longer needed, that refCount should be decremented. This is needed for thread-safety purposes, to allow multiple threads to access this and related functions, while ensuring the results are always valid.

Tcl_FSChdir replaces the library version of chdir(). The path is normalized and then passed to the filesystem which claims it. If that filesystem does not implement this function, Tcl will fallback to a combination of stat and access to check whether the directory exists and has appropriate permissions.

For results, see chdir() documentation. If successful, we keep a record of the successful path in cwdPathPtr for subsequent calls to getcwd.

Tcl_FSPathSeparator returns the separator character to be used for most specific element of the path specified by pathPtr (i.e. the last part of the path).

The separator is returned as a Tcl_Obj containing a string of length 1. If the path is invalid, NULL is returned.

Tcl_FSJoinPath takes the given Tcl_Obj, which should be a valid list, and returns the path object given by considering the first 'elements' elements as valid path segments. If elements < 0, we use the entire list.

Returns object with refCount of zero, containing the joined path.

Tcl_FSSplitPath takes the given Tcl_Obj, which should be a valid path, and returns a Tcl List object containing each segment of that path as an element.

Returns list object with refCount of zero. If the passed in lenPtr is non-NULL, we use it to return the number of elements in the returned list.

Tcl_FSEqualPaths tests whether the two paths given represent the same filesystem object

It returns 1 if the paths are equal, and 0 if they are different. If either path is NULL, 0 is always returned.

Tcl_FSGetNormalizedPath this important function attempts to extract from the given Tcl_Obj a unique normalized path representation, whose string value can be used as a unique identifier for the file.

It returns the normalized path object, with refCount of zero, or NULL if the path was invalid or could otherwise not be successfully converted. Extraction of absolute, normalized paths is very efficient (because the filesystem operates on these representations internally), although the result when the filesystem contains numerous symbolic links may not be the most user-friendly version of a path.

Tcl_FSJoinToPath takes the given object, which should usually be a valid path or NULL, and joins onto it the array of paths segments given.

Returns object with refCount of zero, containing the joined path.

Tcl_FSConvertToPathType tries to convert the given Tcl_Obj to a valid Tcl path type, taking account of the fact that the cwd may have changed even if this object is already supposedly of the correct type. The filename may begin with "~" (to indicate current user's home directory) or "~<user>" (to indicate any user's home directory).

If the conversion succeeds (i.e. the object is a valid path in one of the current filesystems), then TCL_OK is returned. Otherwise TCL_ERROR is returned, and an error message may be left in the interpreter.

Tcl_FSGetInternalRep extracts the internal representation of a given path object, in the given filesystem. If the path object belongs to a different filesystem, we return NULL. If the internal representation is currently NULL, we attempt to generate it, by calling the filesystem's Tcl_FSCreateInternalRepProc.

Returns NULL or a valid internal path representation. This internal representation is cached, so that repeated calls to this function will not require additional conversions.

Tcl_FSGetTranslatedPath attempts to extract the translated path from the given Tcl_Obj.

If the translation succeeds (i.e. the object is a valid path), then it is returned. Otherwise NULL will be returned, and an error message may be left in the interpreter. A "translated" path is one which contains no "~" or "~user" sequences (these have been expanded to their current representation in the filesystem). The object returned is owned by the caller, which must store it or call Tcl_DecrRefCount to ensure memory is freed. This function is of little practical use, and Tcl_FSGetNormalizedPath or Tcl_GetNativePath are usually better functions to use for most purposes.

Tcl_FSGetTranslatedStringPath does the same as Tcl_FSGetTranslatedPath, but returns a character string or NULL. The string returned is dynamically allocated and owned by the caller, which must store it or call ckfree to ensure it is freed. Again, Tcl_FSGetNormalizedPath or Tcl_GetNativePath are usually better functions to use for most purposes.

Tcl_FSNewNativePath performs something like that reverse of the usual obj->path->nativerep conversions. If some code retrieves a path in native form (from, e.g. readlink or a native dialog), and that path is to be used at the Tcl level, then calling this function is an efficient way of creating the appropriate path object type.

The resulting object is a pure 'path' object, which will only receive a Utf-8 string representation if that is required by some Tcl code.

Tcl_FSGetNativePath is for use by the Win/Unix/MacOS native filesystems, so that they can easily retrieve the native (char* or TCHAR*) representation of a path. This function is a convenience wrapper around Tcl_FSGetInternalRep, and assumes the native representation is string-based. It may be desirable in the future to have non-string-based native representations (for example, on MacOS, a representation using a fileSpec of FSRef structure would probably be more efficient). On Windows a full Unicode representation would allow for paths of unlimited length. Currently the representation is simply a character string containing the complete, absolute path in the native encoding.

The native representation is cached so that repeated calls to this function will not require additional conversions.

Tcl_FSFileSystemInfo returns a list of two elements. The first element is the name of the filesystem (e.g. "native" or "vfs" or "zip" or "prowrap", perhaps), and the second is the particular type of the given path within that filesystem (which is filesystem dependent). The second element may be empty if the filesystem does not provide a further categorization of files.

A valid list object is returned, unless the path object is not recognized, when NULL will be returned.

Tcl_FSGetFileSystemForPath returns the a pointer to the Tcl_Filesystem which accepts this path as valid.

If no filesystem will accept the path, NULL is returned.

Tcl_FSGetPathType determines whether the given path is relative to the current directory, relative to the current volume, or absolute.

It returns one of TCL_PATH_ABSOLUTE, TCL_PATH_RELATIVE, or TCL_PATH_VOLUME_RELATIVE

Tcl_AllocStatBuf allocates a Tcl_StatBuf on the system heap (which may be deallocated by being passed to ckfree.) This allows extensions to invoke Tcl_FSStat and Tcl_FSLStat without being dependent on the size of the buffer. That in turn depends on the flags used to build Tcl.

TCL_FILESYSTEM

A filesystem provides a Tcl_Filesystem structure that contains pointers to functions that implement the various operations on a filesystem; these operations are invoked as needed by the generic layer, which generally occurs through the functions listed above.

The Tcl_Filesystem structures are manipulated using the following methods.

Tcl_FSRegister takes a pointer to a filesystem structure and an optional piece of data to associated with that filesystem. On calling this function, Tcl will attach the filesystem to the list of known filesystems, and it will become fully functional immediately. Tcl does not check if the same filesystem is registered multiple times (and in general that is not a good thing to do). TCL_OK will be returned.

Tcl_FSUnregister removes the given filesystem structure from the list of known filesystems, if it is known, and returns TCL_OK. If the filesystem is not currently registered, TCL_ERROR is returned.

Tcl_FSData will return the ClientData associated with the given filesystem, if that filesystem is registered. Otherwise it will return NULL.

Tcl_FSMountsChanged is used to inform the Tcl's core that the set of mount points for the given (already registered) filesystem have changed, and that cached file representations may therefore no longer be correct.

The Tcl_Filesystem structure contains the following fields: typedef struct Tcl_Filesystem {
    CONST char *typeName;
    int structureLength;
    Tcl_FSVersion version;
    Tcl_FSPathInFilesystemProc *pathInFilesystemProc;
    Tcl_FSDupInternalRepProc *dupInternalRepProc;
    Tcl_FSFreeInternalRepProc *freeInternalRepProc;
    Tcl_FSInternalToNormalizedProc *internalToNormalizedProc;
    Tcl_FSCreateInternalRepProc *createInternalRepProc;
    Tcl_FSNormalizePathProc *normalizePathProc;
    Tcl_FSFilesystemPathTypeProc *filesystemPathTypeProc;
    Tcl_FSFilesystemSeparatorProc *filesystemSeparatorProc;
    Tcl_FSStatProc *statProc;
    Tcl_FSAccessProc *accessProc;
    Tcl_FSOpenFileChannelProc *openFileChannelProc;
    Tcl_FSMatchInDirectoryProc *matchInDirectoryProc;
    Tcl_FSUtimeProc *utimeProc;
    Tcl_FSLinkProc *linkProc;
    Tcl_FSListVolumesProc *listVolumesProc;
    Tcl_FSFileAttrStringsProc *fileAttrStringsProc;
    Tcl_FSFileAttrsGetProc *fileAttrsGetProc;
    Tcl_FSFileAttrsSetProc *fileAttrsSetProc;
    Tcl_FSCreateDirectoryProc *createDirectoryProc;
    Tcl_FSRemoveDirectoryProc *removeDirectoryProc;
    Tcl_FSDeleteFileProc *deleteFileProc;
    Tcl_FSCopyFileProc *copyFileProc;
    Tcl_FSRenameFileProc *renameFileProc;
    Tcl_FSCopyDirectoryProc *copyDirectoryProc;
    Tcl_FSLstatProc *lstatProc;
    Tcl_FSLoadFileProc *loadFileProc;
    Tcl_FSGetCwdProc *getCwdProc;
    Tcl_FSChdirProc *chdirProc; } Tcl_Filesystem;

Except for the first three fields in this structure which contain simple data elements, all entries contain addresses of functions called by the generic filesystem layer to perform the complete range of filesystem related actions.

The many functions in this structure are broken down into three categories: infrastructure functions (almost all of which must be implemented), operational functions (which must be implemented if a complete filesystem is provided), and efficiency functions (which need only be implemented if they can be done so efficiently, or if they have side-effects which are required by the filesystem; Tcl has less efficient emulations it can fall back on). It is important to note that, in the current version of Tcl, most of these fallbacks are only used to handle commands initiated in Tcl, not in C. What this means is, that if a 'file rename' command is issued in Tcl, and the relevant filesystem(s) do not implement their Tcl_FSRenameFileProc, Tcl's core will instead fallback on a combination of other filesystem functions (it will use Tcl_FSCopyFileProc followed by Tcl_FSDeleteFileProc, and if Tcl_FSCopyFileProc is not implemented there is a further fallback). However, if a Tcl_FSRenameFile command is issued at the C level, no such fallbacks occur. This is true except for the last four entries in the filesystem table (lstat, load, getcwd and chdir) for which fallbacks do in fact occur at the C level.

As an example, here is the filesystem lookup table used by the "vfs" extension which allows filesystem actions to be implemented in Tcl. static Tcl_Filesystem vfsFilesystem = {
    "tclvfs",
    sizeof(Tcl_Filesystem),
    TCL_FILESYSTEM_VERSION_1,
    &VfsPathInFilesystem,
    &VfsDupInternalRep,
    &VfsFreeInternalRep,
    /* No internal to normalized, since we don't create any
     * pure 'internal' Tcl_Obj path representations */
    NULL,
    /* No create native rep function, since we don't use it
     * and don't choose to support uses of 'Tcl_FSNewNativePath' */
    NULL,
    /* Normalize path isn't needed - we assume paths only have
     * one representation */
    NULL,
    &VfsFilesystemPathType,
    &VfsFilesystemSeparator,
    &VfsStat,
    &VfsAccess,
    &VfsOpenFileChannel,
    &VfsMatchInDirectory,
    &VfsUtime,
    /* We choose not to support symbolic links inside our vfs's */
    NULL,
    &VfsListVolumes,
    &VfsFileAttrStrings,
    &VfsFileAttrsGet,
    &VfsFileAttrsSet,
    &VfsCreateDirectory,
    &VfsRemoveDirectory,
    &VfsDeleteFile,
    /* No copy file - fallback will occur at Tcl level */
    NULL,
    /* No rename file - fallback will occur at Tcl level */
    NULL,
    /* No copy directory - fallback will occur at Tcl level */
    NULL,
    /* Core will use stat for lstat */
    NULL,
    /* No load - fallback on core implementation */
    NULL,
    /* We don't need a getcwd or chdir - fallback on Tcl's versions */
    NULL,
    NULL };

Any functions which take path names in Tcl_Obj form take those names in UTF-8 form. The filesystem infrastructure API is designed to support efficient, cached conversion of these UTF-8 paths to other native representations.

TYPENAME

The typeName field contains a null-terminated string that identifies the type of the filesystem implemented, e.g. native or zip or vfs.

STRUCTURE LENGTH

The structureLength field is generally implemented as sizeof(Tcl_Filesystem), and is there to allow easier binary backwards compatibility if the size of the structure changes in a future Tcl release.

VERSION

The version field should be set to TCL_FILESYSTEM_VERSION_1.

FILESYSTEM INFRASTRUCTURE

These fields contain addresses of functions which are used to associate a particular filesystem with a file path, and deal with the internal handling of path representations, for example copying and freeing such representations.

PATHINFILESYSTEMPROC

The pathInFilesystemProc field contains the address of a function which is called to determine whether a given path object belongs to this filesystem or not. Tcl will only call the rest of the filesystem functions with a path for which this function has returned TCL_OK. If the path does not belong, -1 should be returned (the behaviour of Tcl for any other return value is not defined). If TCL_OK is returned, then the optional clientDataPtr output parameter can be used to return an internal (filesystem specific) representation of the path, which will be cached inside the path object, and may be retrieved efficiently by the other filesystem functions. Tcl will simultaneously cache the fact that this path belongs to this filesystem. Such caches are invalidated when filesystem structures are added or removed from Tcl's internal list of known filesystems.

typedef int Tcl_FSPathInFilesystemProc(
    Tcl_Obj *pathPtr,
    ClientData *clientDataPtr);

DUPINTERNALREPPROC

This function makes a copy of a path's internal representation, and is called when Tcl needs to duplicate a path object. If NULL, Tcl will simply not copy the internal representation, which may then need to be regenerated later.

typedef ClientData Tcl_FSDupInternalRepProc(
    ClientData clientData);

FREEINTERNALREPPROC
Free the internal representation. This must be implemented if internal representations need freeing (i.e. if some memory is allocated when an internal representation is generated), but may otherwise be NULL.

typedef void Tcl_FSFreeInternalRepProc(
    ClientData clientData);

INTERNALTONORMALIZEDPROC

Function to convert internal representation to a normalized path. Only required if the filesystem creates pure path objects with no string/path representation. The return value is a Tcl object whose string representation is the normalized path.

typedef Tcl_Obj* Tcl_FSInternalToNormalizedProc(
    ClientData clientData);

CREATEINTERNALREPPROC

Function to take a path object, and calculate an internal representation for it, and store that native representation in the object. May be NULL if paths have no internal representation, or if the Tcl_FSPathInFilesystemProc for this filesystem always immediately creates an internal representation for paths it accepts.

typedef ClientData Tcl_FSCreateInternalRepProc(
    Tcl_Obj *pathPtr);

NORMALIZEPATHPROC

Function to normalize a path. Should be implemented for all filesystems which can have multiple string representations for the same path object. In Tcl, every 'path' must have a single unique 'normalized' string representation. Depending on the filesystem, there may be more than one unnormalized string representation which refers to that path (e.g. a relative path, a path with different character case if the filesystem is case insensitive, a path contain a reference to a home directory such as '~', a path containing symbolic links, etc). If the very last component in the path is a symbolic link, it should not be converted into the object it points to (but its case or other aspects should be made unique). All other path components should be converted from symbolic links. This one exception is required to agree with Tcl's semantics with 'file delete', 'file rename', 'file copy' operating on symbolic links. This function may be called with 'nextCheckpoint' either at the beginning of the path (i.e. zero), at the end of the path, or at any intermediate file separator in the path. It will never point to any other arbitrary position in the path. In the last of the three valid cases, the implementation can assume that the path up to and including the file separator is known and normalized.

typedef int Tcl_FSNormalizePathProc(
    Tcl_Interp *interp,
    Tcl_Obj *pathPtr,
    int nextCheckpoint);

FILESYSTEM OPERATIONS

The fields in this section of the structure contain addresses of functions which are called to carry out the basic filesystem operations. A filesystem which expects to be used with the complete standard Tcl command set must implement all of these. If some of them are not implemented, then certain Tcl commands may fail when operating on paths within that filesystem. However, in some instances this may be desirable (for example, a read-only filesystem should not implement the last four functions, and a filesystem which does not support symbolic links need not implement the readlink function, etc. The Tcl core expects filesystems to behave in this way).

FILESYSTEMPATHTYPEPROC

Function to determine the type of a path in this filesystem. May be NULL, in which case no type information will be available to users of the filesystem. The 'type' is used only for informational purposes, and should be returned as the string representation of the Tcl_Obj which is returned. A typical return value might be "networked", "zip" or "ftp". The Tcl_Obj result is owned by the filesystem and so Tcl will increment the refCount of that object if it wishes to retain a reference to it.

typedef Tcl_Obj* Tcl_FSFilesystemPathTypeProc(
    Tcl_Obj *pathPtr);

FILESYSTEMSEPARATORPROC

Function to return the separator character(s) for this filesystem. Must be implemented, otherwise the file separator command will not function correctly. The usual return value will be a Tcl_Obj containing the string "/".

typedef Tcl_Obj* Tcl_FSFilesystemSeparatorProc(
    Tcl_Obj *pathPtr);

STATPROC

Function to process a Tcl_FSStat() call. Must be implemented for any reasonable filesystem, since many Tcl level commands depend crucially upon it (e.g. file atime, file isdirectory, file size, glob).

typedef int Tcl_FSStatProc(
    Tcl_Obj *pathPtr,
    Tcl_StatBuf *statPtr);

The Tcl_FSStatProc fills the stat structure statPtr with information about the specified file. You do not need any access rights to the file to get this information but you need search rights to all directories named in the path leading to the file. The stat structure includes info regarding device, inode (always 0 on Windows), privilege mode, nlink (always 1 on Windows), user id (always 0 on Windows), group id (always 0 on Windows), rdev (same as device on Windows), size, last access time, last modification time, and creation time.

If the file represented by pathPtr exists, the Tcl_FSStatProc returns 0 and the stat structure is filled with data. Otherwise, -1 is returned, and no stat info is given.

ACCESSPROC

Function to process a Tcl_FSAccess() call. Must be implemented for any reasonable filesystem, since many Tcl level commands depend crucially upon it (e.g. file exists, file readable).

typedef int Tcl_FSAccessProc(
    Tcl_Obj *pathPtr,
    int mode);

The Tcl_FSAccessProc checks whether the process would be allowed to read, write or test for existence of the file (or other file system object) whose name is pathname. If pathname is a symbolic link, then permissions of the file referred by this symbolic link should be tested.

On success (all requested permissions granted), zero is returned. On error (at least one bit in mode asked for a permission that is denied, or some other error occurred), -1 is returned.

OPENFILECHANNELPROC

Function to process a Tcl_FSOpenFileChannel() call. Must be implemented for any reasonable filesystem, since any operations which require open or accessing a file's contents will use it (e.g. open, encoding, and many Tk commands).

typedef Tcl_Channel Tcl_FSOpenFileChannelProc(
    Tcl_Interp *interp,
    Tcl_Obj *pathPtr,
    int mode,
    int permissions);

The Tcl_FSOpenFileChannelProc opens a file specified by pathPtr and returns a channel handle that can be used to perform input and output on the file. This API is modeled after the fopen procedure of the Unix standard I/O library. The syntax and meaning of all arguments is similar to those given in the Tcl open command when opening a file, where the mode argument is a combination of the POSIX flags O_RDONLY, O_WRONLY, etc. If an error occurs while opening the channel, the Tcl_FSOpenFileChannelProc returns NULL and records a POSIX error code that can be retrieved with Tcl_GetErrno. In addition, if interp is non-NULL, the Tcl_FSOpenFileChannelProc leaves an error message in interp's result after any error.

The newly created channel is not registered in the supplied interpreter; to register it, use Tcl_RegisterChannel. If one of the standard channels, stdin, stdout or stderr was previously closed, the act of creating the new channel also assigns it as a replacement for the standard channel.

MATCHINDIRECTORYPROC

Function to process a Tcl_FSMatchInDirectory() call. If not implemented, then glob and recursive copy functionality will be lacking in the filesystem (and this may impact commands like 'encoding names' which use glob functionality internally).

typedef int Tcl_FSMatchInDirectoryProc(
    Tcl_Interp* interp,
    Tcl_Obj *result,
    Tcl_Obj *pathPtr,
    CONST char *pattern,
    Tcl_GlobTypeData * types);

The function should return all files or directories (or other filesystem objects) which match the given pattern and accord with the types specification given. There are two ways in which this function may be called. If pattern is NULL, then pathPtr is a full path specification of a single file or directory which should be checked for existence and correct type. Otherwise, pathPtr is a directory, the contents of which the function should search for files or directories which have the correct type. In either case, pathPtr can be assumed to be both non-NULL and non-empty. It is not currently documented whether pathPtr will have a file separator at its end of not, so code should be flexible to both possibilities.

The return value is a standard Tcl result indicating whether an error occurred in the matching process. Error messages are placed in interp, but on a TCL_OK result, the interpreter should not be modified, but rather results should be added to the result object given (which can be assumed to be a valid Tcl list). The matches added to result should include any path prefix given in pathPtr (this usually means they will be absolute path specifications). Note that if no matches are found, that simply leads to an empty result --- errors are only signaled for actual file or filesystem problems which may occur during the matching process.

UTIMEPROC

Function to process a Tcl_FSUtime() call. Required to allow setting (not reading) of times with 'file mtime', 'file atime' and the open-r/open-w/fcopy implementation of 'file copy'.

typedef int Tcl_FSUtimeProc(
    Tcl_Obj *pathPtr,
    struct utimbuf *tval);

The access and modification times of the file specified by pathPtr should be changed to the values given in the tval structure.

The return value is a standard Tcl result indicating whether an error occurred in the process.

LINKPROC

Function to process a Tcl_FSLink() call. Should be implemented only if the filesystem supports links, and may otherwise be NULL.

typedef Tcl_Obj* Tcl_FSLinkProc(
    Tcl_Obj *linkNamePtr,
    Tcl_Obj *toPtr,
    int linkAction);

If toPtr is NULL, the function is being asked to read the contents of a link. The result is a Tcl_Obj specifying the contents of the link given by linkNamePtr, or NULL if the link could not be read. The result is owned by the caller, which should call Tcl_DecrRefCount when the result is no longer needed. If toPtr is not NULL, the function should attempt to create a link. The result in this case should be toPtr if the link was successful and NULL otherwise. In this case the result is not owned by the caller. See the documentation for Tcl_FSLink for the correct interpretation of the linkAction flags.

LISTVOLUMESPROC

Function to list any filesystem volumes added by this filesystem. Should be implemented only if the filesystem adds volumes at the head of the filesystem, so that they can be returned by 'file volumes'.

typedef Tcl_Obj* Tcl_FSListVolumesProc(void);

The result should be a list of volumes added by this filesystem, or NULL (or an empty list) if no volumes are provided. The result object is considered to be owned by the filesystem (not by Tcl's core), but should be given a refCount for Tcl. Tcl will use the contents of the list and then decrement that refCount. This allows filesystems to choose whether they actually want to retain a 'master list' of volumes or not (if not, they generate the list on the fly and pass it to Tcl with a refCount of 1 and then forget about the list, if yes, then they simply increment the refCount of their master list and pass it to Tcl which will copy the contents and then decrement the count back to where it was).

Therefore, Tcl considers return values from this proc to be read-only.

FILEATTRSTRINGSPROC

Function to list all attribute strings which are valid for this filesystem. If not implemented the filesystem will not support the file attributes command. This allows arbitrary additional information to be attached to files in the filesystem. If it is not implemented, there is no need to implement the get and set methods.

typedef CONST char** Tcl_FSFileAttrStringsProc(
    Tcl_Obj *pathPtr,
    Tcl_Obj** objPtrRef);

The called function may either return an array of strings, or may instead return NULL and place a Tcl list into the given objPtrRef. Tcl will take that list and first increment its refCount before using it. On completion of that use, Tcl will decrement its refCount. Hence if the list should be disposed of by Tcl when done, it should have a refCount of zero, and if the list should not be disposed of, the filesystem should ensure it retains a refCount on the object.

FILEATTRSGETPROC

Function to process a Tcl_FSFileAttrsGet() call, used by 'file attributes'.

typedef int Tcl_FSFileAttrsGetProc(
    Tcl_Interp *interp,
    int index,
    Tcl_Obj *pathPtr,
    Tcl_Obj **objPtrRef);

Returns a standard Tcl return code. The attribute value retrieved, which corresponds to the index'th element in the list returned by the Tcl_FSFileAttrStringsProc, is a Tcl_Obj placed in objPtrRef (if TCL_OK was returned) and is likely to have a refCount of zero. Either way we must either store it somewhere (e.g. the Tcl result), or Incr/Decr its refCount to ensure it is properly freed.

FILEATTRSSETPROC

Function to process a Tcl_FSFileAttrsSet() call, used by 'file attributes'. If the filesystem is read-only, there is no need to implement this.

typedef int Tcl_FSFileAttrsSetProc(
    Tcl_Interp *interp,
    int index,
    Tcl_Obj *pathPtr,
    Tcl_Obj *objPtr);

The attribute value of the index'th element in the list returned by the Tcl_FSFileAttrStringsProc should be set to the objPtr given.

CREATEDIRECTORYPROC

Function to process a Tcl_FSCreateDirectory() call. Should be implemented unless the FS is read-only.

typedef int Tcl_FSCreateDirectoryProc(
    Tcl_Obj *pathPtr);

The return value is a standard Tcl result indicating whether an error occurred in the process. If successful, a new directory should have been added to the filesystem in the location specified by pathPtr.

REMOVEDIRECTORYPROC

Function to process a 'Tcl_FSRemoveDirectory()' call. Should be implemented unless the FS is read-only.

typedef int Tcl_FSRemoveDirectoryProc(
    Tcl_Obj *pathPtr,
    int recursive,
    Tcl_Obj **errorPtr);

The return value is a standard Tcl result indicating whether an error occurred in the process. If successful, the directory specified by pathPtr should have been removed from the filesystem. If the recursive flag is given, then a non-empty directory should be deleted without error. If an error does occur, the name of the file or directory which caused the error should be placed in errorPtr.

DELETEFILEPROC

Function to process a Tcl_FSDeleteFile() call. Should be implemented unless the FS is read-only.

typedef int Tcl_FSDeleteFileProc(
    Tcl_Obj *pathPtr);

The return value is a standard Tcl result indicating whether an error occurred in the process. If successful, the file specified by pathPtr should have been removed from the filesystem. Note that, if the filesystem supports symbolic links, Tcl will always call this function and not Tcl_FSRemoveDirectoryProc when needed to delete them (even if they are symbolic links to directories).

FILESYSTEM EFFICIENCY

LSTATPROC

Function to process a Tcl_FSLstat() call. If not implemented, Tcl will attempt to use the statProc defined above instead. Therefore it need only be implemented if a filesystem can differentiate between stat and lstat calls.

typedef int Tcl_FSLstatProc(
    Tcl_Obj *pathPtr,
    Tcl_StatBuf *statPtr);

The behavior of this function is very similar to that of the Tcl_FSStatProc defined above, except that if it is applied to a symbolic link, it returns information about the link, not about the target file.

COPYFILEPROC

Function to process a Tcl_FSCopyFile() call. If not implemented Tcl will fall back on open-r, open-w and fcopy as a copying mechanism. Therefore it need only be implemented if the filesystem can perform that action more efficiently.

typedef int Tcl_FSCopyFileProc(
    Tcl_Obj *srcPathPtr,
    Tcl_Obj *destPathPtr);

The return value is a standard Tcl result indicating whether an error occurred in the copying process. Note that, destPathPtr is the name of the file which should become the copy of srcPathPtr. It is never the name of a directory into which srcPathPtr could be copied (i.e. the function is much simpler than the Tcl level 'file copy' subcommand). Note that, if the filesystem supports symbolic links, Tcl will always call this function and not Tcl_FSCopyDirectoryProc when needed to copy them (even if they are symbolic links to directories).

RENAMEFILEPROC

Function to process a Tcl_FSRenameFile() call. If not implemented, Tcl will fall back on a copy and delete mechanism. Therefore it need only be implemented if the filesystem can perform that action more efficiently.

typedef int Tcl_FSRenameFileProc(
    Tcl_Obj *srcPathPtr,
    Tcl_Obj *destPathPtr);

The return value is a standard Tcl result indicating whether an error occurred in the renaming process.

COPYDIRECTORYPROC

Function to process a Tcl_FSCopyDirectory() call. If not implemented, Tcl will fall back on a recursive create-dir, file copy mechanism. Therefore it need only be implemented if the filesystem can perform that action more efficiently.

typedef int Tcl_FSCopyDirectoryProc(
    Tcl_Obj *srcPathPtr,
    Tcl_Obj *destPathPtr,
    Tcl_Obj **errorPtr);

The return value is a standard Tcl result indicating whether an error occurred in the copying process. If an error does occur, the name of the file or directory which caused the error should be placed in errorPtr. Note that, destPathPtr is the name of the directory-name which should become the mirror-image of srcPathPtr. It is not the name of a directory into which srcPathPtr should be copied (i.e. the function is much simpler than the Tcl level 'file copy' subcommand).

LOADFILEPROC

Function to process a Tcl_FSLoadFile() call. If not implemented, Tcl will fall back on a copy to native-temp followed by a Tcl_FSLoadFile on that temporary copy. Therefore it need only be implemented if the filesystem can load code directly, or it can be implemented simply to return TCL_ERROR to disable load functionality in this filesystem entirely.

typedef int Tcl_FSLoadFileProc(
    Tcl_Interp * interp,
    Tcl_Obj *pathPtr,
    Tcl_LoadHandle * handlePtr,
    Tcl_FSUnloadFileProc * unloadProcPtr);

Returns a standard Tcl completion code. If an error occurs, an error message is left in the interp's result. The function dynamically loads a binary code file into memory. On a successful load, the handlePtr should be filled with a token for the dynamically loaded file, and the unloadProcPtr should be filled in with the address of a procedure. The procedure will be called with the given Tcl_LoadHandle as its only parameter when Tcl needs to unload the file.

UNLOADFILEPROC

Function to unload a previously successfully loaded file. If load was implemented, then this should also be implemented, if there is any cleanup action required.

typedef void Tcl_FSUnloadFileProc(
    Tcl_LoadHandle loadHandle);

GETCWDPROC

Function to process a Tcl_FSGetCwd() call. Most filesystems need not implement this. It will usually only be called once, if 'getcwd' is called before 'chdir'. May be NULL.

typedef Tcl_Obj* Tcl_FSGetCwdProc(
    Tcl_Interp *interp);

If the filesystem supports a native notion of a current working directory (which might perhaps change independent of Tcl), this function should return that cwd as the result, or NULL if the current directory could not be determined (e.g. the user does not have appropriate permissions on the cwd directory). If NULL is returned, an error message is left in the interp's result.

CHDIRPROC

Function to process a Tcl_FSChdir() call. If filesystems do not implement this, it will be emulated by a series of directory access checks. Otherwise, virtual filesystems which do implement it need only respond with a positive return result if the dirName is a valid, accessible directory in their filesystem. They need not remember the result, since that will be automatically remembered for use by GetCwd. Real filesystems should carry out the correct action (i.e. call the correct system 'chdir' api).

typedef int Tcl_FSChdirProc(
    Tcl_Obj *pathPtr);

The Tcl_FSChdirProc changes the applications current working directory to the value specified in pathPtr. The function returns -1 on error or 0 on success.

KEYWORDS
stat access filesystem vfs