FS_SNAPSHOT_CREATE(2) System Calls Manual FS_SNAPSHOT_CREATE(2)

fs_snapshot_create — create read only snapshot of a mounted filesystem

#include <sys/attr.h>
#include <sys/snapshot.h>


int
fs_snapshot_create(int dirfd, const char * name, uint32_t flags);

int
fs_snapshot_delete(int dirfd, const char * name, uint32_t flags);

int
fs_snapshot_list(int dirfd, struct attrlist * name, void * attrbuf, size_t bufsize, uint32_t flags);

int
fs_snapshot_rename(int dirfd, const char * old, const char * new, uint32_t flags);

int
fs_snapshot_mount(int dirfd, const char * dir, const char * snapshot, uint32_t flags);

int
fs_snapshot_revert(int dirfd, const char * name, uint32_t flags);

The () function, for supported Filesystems, causes a snapshot of the Filesystem to be created. A snapshot is a read only copy of the filesystem frozen at a point in time. The Filesystem is identified by the dirfd parameter which should be a file descriptor associated with the root directory of the filesystem for which the snapshot is to be created. name can be any valid name for a component name (except . and ..). The () function causes the named snapshot name to be deleted and the () function causes the named snapshot old to be renamed to the name new. Available snapshots along with their attributes can be listed by calling () which is to be used in exactly the same way as getattrlistbulk(2).

Snapshots may be useful for backing up the Filesystem and to restore the Filesystem to a previous state. Snapshots are expected to consume no additional storage on creation but might consume additional storage as the active Filesystem is modified. Similarly deletion of files on the active filesystem may not result in the storage being available if the snapshot contains the file. Additionally, the underlying Filesystem may impose a limit on the number of snapshots that can be taken. For supporting Filesystems, a snapshot may be used as a source for a mount. This can be done by the () function. The snapshot will be mounted read only. When a snapshot is mounted, it cannot be deleted but it can be renamed. To revert the filesystem to a previous snapshot, the () can be used. It should be noted that reverting a filesystem to a snapshot is a destructive operation and causes all changes made to the filesystem (including snapshots created after the snapshot being reverted to) to be lost.

All snapshot functions require superuser privileges and also require an additional entitlement.

The flags parameter specifies the options that can be passed. only () options are currently defined:

File system is not appropriate path to user data.
Treats all files on the disk as though they are owned by the current user, no matter who actually owns them.
Don't follow symlink when resolving mount point.

Upon successful completion, fs_snapshot_create() , fs_snapshot_delete() and fs_snapshot_rename() returns 0. Otherwise, a value of -1 is returned and errno is set to indicate the error. fs_snapshot_list() returns the number of entries successfully read. A return value of 0 indicates there are no more entries. Otherwise, a value of -1 is returned and errno is set to indicate the error. Return values are the same as getattrlistbulk(2).

Not all volumes support snapshots. A volume can be tested for snapshot support by using getattrlist(2) to get the volume capabilities attribute ATTR_VOL_CAPABILITIES, and then testing the VOL_CAP_INT_SNAPSHOT flag.

The fs_snapshot_create() , fs_snapshot_delete() , fs_snapshot_rename() and fs_snapshot_list() function will fail if:

[]
Read permissions are denied for the caller on the filesystem
[]
The underlying filesystem does not support this call.
[]
The value of the flags parameter is invalid.
[]
There is no free space remaining on the file system containing the file.
[]
The limit for the maximum number of snapshots for a filesystem has been reached.
[]
An I/O error occurred while reading from or writing to the file system.
[]
The calling process does not have appropriate privileges.
[]
The requested operation requires modifications in a read-only file system.
[]
The length of a component of a pathname is longer than {NAME_MAX}.
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dirfd is not a valid file descriptor.
[]
dirfd is a file descriptor associated with a non-directory file.

In addition, the fs_snapshot_create() or fs_snapshot_rename() functions may fail with the following errors

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The The named snapshot to be created already exists or the new name already exists for the snapshot being renamed.

fs_snapshot_create() or fs_snapshot_rename() functions may fail with the following errors

[]
The named snapshot does not exist.

fs_snapshot_delete() function may fail with

[]
The named snapshot is currently mounted.

getattrlist(2), getattrlistbulk(2)

The fs_snapshot_create() , fs_snapshot_delete() , fs_snapshot_list() , fs_snapshot_mount() , fs_snapshot_rename() and fs_snapshot_revert() function calls appeared in macOS version 10.13

July 4th, 2017 Darwin