libfuse
Data Fields
fuse_operations Struct Reference

#include <fuse.h>

Data Fields

int(* getattr )(const char *, struct stat *, struct fuse_file_info *fi)
 
int(* readlink )(const char *, char *, size_t)
 
int(* mknod )(const char *, mode_t, dev_t)
 
int(* mkdir )(const char *, mode_t)
 
int(* unlink )(const char *)
 
int(* rmdir )(const char *)
 
int(* symlink )(const char *, const char *)
 
int(* rename )(const char *, const char *, unsigned int)
 
int(* link )(const char *, const char *)
 
int(* chmod )(const char *, mode_t, struct fuse_file_info *fi)
 
int(* chown )(const char *, uid_t, gid_t, struct fuse_file_info *fi)
 
int(* truncate )(const char *, off_t, struct fuse_file_info *fi)
 
int(* open )(const char *, struct fuse_file_info *)
 
int(* read )(const char *, char *, size_t, off_t, struct fuse_file_info *)
 
int(* write )(const char *, const char *, size_t, off_t, struct fuse_file_info *)
 
int(* statfs )(const char *, struct statvfs *)
 
int(* flush )(const char *, struct fuse_file_info *)
 
int(* release )(const char *, struct fuse_file_info *)
 
int(* fsync )(const char *, int, struct fuse_file_info *)
 
int(* setxattr )(const char *, const char *, const char *, size_t, int)
 
int(* getxattr )(const char *, const char *, char *, size_t)
 
int(* listxattr )(const char *, char *, size_t)
 
int(* removexattr )(const char *, const char *)
 
int(* opendir )(const char *, struct fuse_file_info *)
 
int(* readdir )(const char *, void *, fuse_fill_dir_t, off_t, struct fuse_file_info *, enum fuse_readdir_flags)
 
int(* releasedir )(const char *, struct fuse_file_info *)
 
int(* fsyncdir )(const char *, int, struct fuse_file_info *)
 
void *(* init )(struct fuse_conn_info *conn, struct fuse_config *cfg)
 
void(* destroy )(void *)
 
int(* access )(const char *, int)
 
int(* create )(const char *, mode_t, struct fuse_file_info *)
 
int(* lock )(const char *, struct fuse_file_info *, int cmd, struct flock *)
 
int(* utimens )(const char *, const struct timespec tv[2], struct fuse_file_info *fi)
 
int(* bmap )(const char *, size_t blocksize, uint64_t *idx)
 
int(* ioctl )(const char *, int cmd, void *arg, struct fuse_file_info *, unsigned int flags, void *data)
 
int(* poll )(const char *, struct fuse_file_info *, struct fuse_pollhandle *ph, unsigned *reventsp)
 
int(* write_buf )(const char *, struct fuse_bufvec *buf, off_t off, struct fuse_file_info *)
 
int(* read_buf )(const char *, struct fuse_bufvec **bufp, size_t size, off_t off, struct fuse_file_info *)
 
int(* flock )(const char *, struct fuse_file_info *, int op)
 
int(* fallocate )(const char *, int, off_t, off_t, struct fuse_file_info *)
 

Detailed Description

The file system operations:

Most of these should work very similarly to the well known UNIX file system operations. A major exception is that instead of returning an error in 'errno', the operation should return the negated error value (-errno) directly.

All methods are optional, but some are essential for a useful filesystem (e.g. getattr). Open, flush, release, fsync, opendir, releasedir, fsyncdir, access, create, truncate, lock, init and destroy are special purpose methods, without which a full featured filesystem can still be implemented.

In general, all methods are expected to perform any necessary permission checking. However, a filesystem may delegate this task to the kernel by passing the default_permissions mount option to fuse_new(). In this case, methods will only be called if the kernel's permission check has succeeded.

Almost all operations take a path which can be of any length.

Field Documentation

int(* fuse_operations::access)(const char *, int)

Check file access permissions

This will be called for the access() system call. If the 'default_permissions' mount option is given, this method is not called.

This method is not called under Linux kernel versions 2.4.x

int(* fuse_operations::bmap)(const char *, size_t blocksize, uint64_t *idx)

Map block index within file to block index within device

Note: This makes sense only for block device backed filesystems mounted with the 'blkdev' option

int(* fuse_operations::chmod)(const char *, mode_t, struct fuse_file_info *fi)

Change the permission bits of a file

fi will always be NULL if the file is not currenly open, but may also be NULL if the file is open.

int(* fuse_operations::chown)(const char *, uid_t, gid_t, struct fuse_file_info *fi)

Change the owner and group of a file

fi will always be NULL if the file is not currenly open, but may also be NULL if the file is open.

Unless FUSE_CAP_HANDLE_KILLPRIV is disabled, this method is expected to reset the setuid and setgid bits.

int(* fuse_operations::create)(const char *, mode_t, struct fuse_file_info *)

Create and open a file

If the file does not exist, first create it with the specified mode, and then open it.

If this method is not implemented or under Linux kernel versions earlier than 2.6.15, the mknod() and open() methods will be called instead.

void(* fuse_operations::destroy)(void *)

Clean up filesystem

Called on filesystem exit.

int(* fuse_operations::fallocate)(const char *, int, off_t, off_t, struct fuse_file_info *)

Allocates space for an open file

This function ensures that required space is allocated for specified file. If this function returns success then any subsequent write request to specified range is guaranteed not to fail because of lack of space on the file system media.

int(* fuse_operations::flock)(const char *, struct fuse_file_info *, int op)

Perform BSD file locking operation

The op argument will be either LOCK_SH, LOCK_EX or LOCK_UN

Nonblocking requests will be indicated by ORing LOCK_NB to the above operations

For more information see the flock(2) manual page.

Additionally fi->owner will be set to a value unique to this open file. This same value will be supplied to ->release() when the file is released.

Note: if this method is not implemented, the kernel will still allow file locking to work locally. Hence it is only interesting for network filesystems and similar.

int(* fuse_operations::flush)(const char *, struct fuse_file_info *)

Possibly flush cached data

BIG NOTE: This is not equivalent to fsync(). It's not a request to sync dirty data.

Flush is called on each close() of a file descriptor. So if a filesystem wants to return write errors in close() and the file has cached dirty data, this is a good place to write back data and return any errors. Since many applications ignore close() errors this is not always useful.

NOTE: The flush() method may be called more than once for each open(). This happens if more than one file descriptor refers to an opened file due to dup(), dup2() or fork() calls. It is not possible to determine if a flush is final, so each flush should be treated equally. Multiple write-flush sequences are relatively rare, so this shouldn't be a problem.

Filesystems shouldn't assume that flush will always be called after some writes, or that if will be called at all.

int(* fuse_operations::fsync)(const char *, int, struct fuse_file_info *)

Synchronize file contents

If the datasync parameter is non-zero, then only the user data should be flushed, not the meta data.

int(* fuse_operations::fsyncdir)(const char *, int, struct fuse_file_info *)

Synchronize directory contents

If the datasync parameter is non-zero, then only the user data should be flushed, not the meta data

int(* fuse_operations::getattr)(const char *, struct stat *, struct fuse_file_info *fi)

Get file attributes.

Similar to stat(). The 'st_dev' and 'st_blksize' fields are ignored. The 'st_ino' field is ignored except if the 'use_ino' mount option is given. In that case it is passed to userspace, but libfuse and the kernel will still assign a different inode for internal use (called the "nodeid").

fi will always be NULL if the file is not currenly open, but may also be NULL if the file is open.

int(* fuse_operations::getxattr)(const char *, const char *, char *, size_t)

Get extended attributes

void*(* fuse_operations::init)(struct fuse_conn_info *conn, struct fuse_config *cfg)

Initialize filesystem

The return value will passed in the private_data field of fuse_context to all file operations and as a parameter to the destroy() method.

int(* fuse_operations::ioctl)(const char *, int cmd, void *arg, struct fuse_file_info *, unsigned int flags, void *data)

Ioctl

flags will have FUSE_IOCTL_COMPAT set for 32bit ioctls in 64bit environment. The size and direction of data is determined by IOC*() decoding of cmd. For _IOC_NONE, data will be NULL, for _IOC_WRITE data is out area, for _IOC_READ in area and if both are set in/out area. In all non-NULL cases, the area is of _IOC_SIZE(cmd) bytes.

If flags has FUSE_IOCTL_DIR then the fuse_file_info refers to a directory file handle.

int(* fuse_operations::link)(const char *, const char *)

Create a hard link to a file

int(* fuse_operations::listxattr)(const char *, char *, size_t)

List extended attributes

int(* fuse_operations::lock)(const char *, struct fuse_file_info *, int cmd, struct flock *)

Perform POSIX file locking operation

The cmd argument will be either F_GETLK, F_SETLK or F_SETLKW.

For the meaning of fields in 'struct flock' see the man page for fcntl(2). The l_whence field will always be set to SEEK_SET.

For checking lock ownership, the 'fuse_file_info->owner' argument must be used.

For F_GETLK operation, the library will first check currently held locks, and if a conflicting lock is found it will return information without calling this method. This ensures, that for local locks the l_pid field is correctly filled in. The results may not be accurate in case of race conditions and in the presence of hard links, but it's unlikely that an application would rely on accurate GETLK results in these cases. If a conflicting lock is not found, this method will be called, and the filesystem may fill out l_pid by a meaningful value, or it may leave this field zero.

For F_SETLK and F_SETLKW the l_pid field will be set to the pid of the process performing the locking operation.

Note: if this method is not implemented, the kernel will still allow file locking to work locally. Hence it is only interesting for network filesystems and similar.

int(* fuse_operations::mkdir)(const char *, mode_t)

Create a directory

Note that the mode argument may not have the type specification bits set, i.e. S_ISDIR(mode) can be false. To obtain the correct directory type bits use mode|S_IFDIR

int(* fuse_operations::mknod)(const char *, mode_t, dev_t)

Create a file node

This is called for creation of all non-directory, non-symlink nodes. If the filesystem defines a create() method, then for regular files that will be called instead.

int(* fuse_operations::open)(const char *, struct fuse_file_info *)

File open operation

No creation (O_CREAT, O_EXCL) and by default also no truncation (O_TRUNC) flags will be passed to open(). If an application specifies O_TRUNC, fuse first calls truncate() and then open(). Only if 'atomic_o_trunc' has been specified and kernel version is 2.6.24 or later, O_TRUNC is passed on to open.

Unless the 'default_permissions' mount option is given, open should check if the operation is permitted for the given flags. Optionally open may also return an arbitrary filehandle in the fuse_file_info structure, which will be passed to all file operations.

int(* fuse_operations::opendir)(const char *, struct fuse_file_info *)

Open directory

Unless the 'default_permissions' mount option is given, this method should check if opendir is permitted for this directory. Optionally opendir may also return an arbitrary filehandle in the fuse_file_info structure, which will be passed to readdir, closedir and fsyncdir.

int(* fuse_operations::poll)(const char *, struct fuse_file_info *, struct fuse_pollhandle *ph, unsigned *reventsp)

Poll for IO readiness events

Note: If ph is non-NULL, the client should notify when IO readiness events occur by calling fuse_notify_poll() with the specified ph.

Regardless of the number of times poll with a non-NULL ph is received, single notification is enough to clear all. Notifying more times incurs overhead but doesn't harm correctness.

The callee is responsible for destroying ph with fuse_pollhandle_destroy() when no longer in use.

int(* fuse_operations::read)(const char *, char *, size_t, off_t, struct fuse_file_info *)

Read data from an open file

Read should return exactly the number of bytes requested except on EOF or error, otherwise the rest of the data will be substituted with zeroes. An exception to this is when the 'direct_io' mount option is specified, in which case the return value of the read system call will reflect the return value of this operation.

int(* fuse_operations::read_buf)(const char *, struct fuse_bufvec **bufp, size_t size, off_t off, struct fuse_file_info *)

Store data from an open file in a buffer

Similar to the read() method, but data is stored and returned in a generic buffer.

No actual copying of data has to take place, the source file descriptor may simply be stored in the buffer for later data transfer.

The buffer must be allocated dynamically and stored at the location pointed to by bufp. If the buffer contains memory regions, they too must be allocated using malloc(). The allocated memory will be freed by the caller.

int(* fuse_operations::readdir)(const char *, void *, fuse_fill_dir_t, off_t, struct fuse_file_info *, enum fuse_readdir_flags)

Read directory

The filesystem may choose between two modes of operation:

1) The readdir implementation ignores the offset parameter, and passes zero to the filler function's offset. The filler function will not return '1' (unless an error happens), so the whole directory is read in a single readdir operation.

2) The readdir implementation keeps track of the offsets of the directory entries. It uses the offset parameter and always passes non-zero offset to the filler function. When the buffer is full (or an error happens) the filler function will return '1'.

int(* fuse_operations::readlink)(const char *, char *, size_t)

Read the target of a symbolic link

The buffer should be filled with a null terminated string. The buffer size argument includes the space for the terminating null character. If the linkname is too long to fit in the buffer, it should be truncated. The return value should be 0 for success.

int(* fuse_operations::release)(const char *, struct fuse_file_info *)

Release an open file

Release is called when there are no more references to an open file: all file descriptors are closed and all memory mappings are unmapped.

For every open() call there will be exactly one release() call with the same flags and file descriptor. It is possible to have a file opened more than once, in which case only the last release will mean, that no more reads/writes will happen on the file. The return value of release is ignored.

int(* fuse_operations::releasedir)(const char *, struct fuse_file_info *)

Release directory

int(* fuse_operations::removexattr)(const char *, const char *)

Remove extended attributes

int(* fuse_operations::rename)(const char *, const char *, unsigned int)

Rename a file

int(* fuse_operations::rmdir)(const char *)

Remove a directory

int(* fuse_operations::setxattr)(const char *, const char *, const char *, size_t, int)

Set extended attributes

int(* fuse_operations::statfs)(const char *, struct statvfs *)

Get file system statistics

The 'f_favail', 'f_fsid' and 'f_flag' fields are ignored

int(* fuse_operations::symlink)(const char *, const char *)

Create a symbolic link

int(* fuse_operations::truncate)(const char *, off_t, struct fuse_file_info *fi)

Change the size of a file

fi will always be NULL if the file is not currenly open, but may also be NULL if the file is open.

Unless FUSE_CAP_HANDLE_KILLPRIV is disabled, this method is expected to reset the setuid and setgid bits.

int(* fuse_operations::unlink)(const char *)

Remove a file

int(* fuse_operations::utimens)(const char *, const struct timespec tv[2], struct fuse_file_info *fi)

Change the access and modification times of a file with nanosecond resolution

This supersedes the old utime() interface. New applications should use this.

fi will always be NULL if the file is not currenly open, but may also be NULL if the file is open.

See the utimensat(2) man page for details.

int(* fuse_operations::write)(const char *, const char *, size_t, off_t, struct fuse_file_info *)

Write data to an open file

Write should return exactly the number of bytes requested except on error. An exception to this is when the 'direct_io' mount option is specified (see read operation).

Unless FUSE_CAP_HANDLE_KILLPRIV is disabled, this method is expected to reset the setuid and setgid bits.

int(* fuse_operations::write_buf)(const char *, struct fuse_bufvec *buf, off_t off, struct fuse_file_info *)

Write contents of buffer to an open file

Similar to the write() method, but data is supplied in a generic buffer. Use fuse_buf_copy() to transfer data to the destination.

Unless FUSE_CAP_HANDLE_KILLPRIV is disabled, this method is expected to reset the setuid and setgid bits.


The documentation for this struct was generated from the following file: