diff options
| -rw-r--r-- | Documentation/filesystems/fiemap.rst (renamed from Documentation/filesystems/fiemap.txt) | 135 | ||||
| -rw-r--r-- | Documentation/filesystems/index.rst | 1 |
2 files changed, 70 insertions, 66 deletions
diff --git a/Documentation/filesystems/fiemap.txt b/Documentation/filesystems/fiemap.rst index ac87e6fda842..2a572e7edc08 100644 --- a/Documentation/filesystems/fiemap.txt +++ b/Documentation/filesystems/fiemap.rst @@ -1,3 +1,5 @@ +.. SPDX-License-Identifier: GPL-2.0 + ============ Fiemap Ioctl ============ @@ -10,9 +12,9 @@ returns a list of extents. Request Basics -------------- -A fiemap request is encoded within struct fiemap: +A fiemap request is encoded within struct fiemap:: -struct fiemap { + struct fiemap { __u64 fm_start; /* logical offset (inclusive) at * which to start mapping (in) */ __u64 fm_length; /* logical length of mapping which @@ -23,7 +25,7 @@ struct fiemap { __u32 fm_extent_count; /* size of fm_extents array (in) */ __u32 fm_reserved; struct fiemap_extent fm_extents[0]; /* array of mapped extents (out) */ -}; + }; fm_start, and fm_length specify the logical range within the file @@ -51,12 +53,12 @@ nothing to prevent the file from changing between calls to FIEMAP. The following flags can be set in fm_flags: -* FIEMAP_FLAG_SYNC -If this flag is set, the kernel will sync the file before mapping extents. +FIEMAP_FLAG_SYNC + If this flag is set, the kernel will sync the file before mapping extents. -* FIEMAP_FLAG_XATTR -If this flag is set, the extents returned will describe the inodes -extended attribute lookup tree, instead of its data tree. +FIEMAP_FLAG_XATTR + If this flag is set, the extents returned will describe the inodes + extended attribute lookup tree, instead of its data tree. Extent Mapping @@ -75,18 +77,18 @@ complete the requested range and will not have the FIEMAP_EXTENT_LAST flag set (see the next section on extent flags). Each extent is described by a single fiemap_extent structure as -returned in fm_extents. - -struct fiemap_extent { - __u64 fe_logical; /* logical offset in bytes for the start of - * the extent */ - __u64 fe_physical; /* physical offset in bytes for the start - * of the extent */ - __u64 fe_length; /* length in bytes for the extent */ - __u64 fe_reserved64[2]; - __u32 fe_flags; /* FIEMAP_EXTENT_* flags for this extent */ - __u32 fe_reserved[3]; -}; +returned in fm_extents:: + + struct fiemap_extent { + __u64 fe_logical; /* logical offset in bytes for the start of + * the extent */ + __u64 fe_physical; /* physical offset in bytes for the start + * of the extent */ + __u64 fe_length; /* length in bytes for the extent */ + __u64 fe_reserved64[2]; + __u32 fe_flags; /* FIEMAP_EXTENT_* flags for this extent */ + __u32 fe_reserved[3]; + }; All offsets and lengths are in bytes and mirror those on disk. It is valid for an extents logical offset to start before the request or its logical @@ -114,26 +116,27 @@ worry about all present and future flags which might imply unaligned data. Note that the opposite is not true - it would be valid for FIEMAP_EXTENT_NOT_ALIGNED to appear alone. -* FIEMAP_EXTENT_LAST -This is generally the last extent in the file. A mapping attempt past -this extent may return nothing. Some implementations set this flag to -indicate this extent is the last one in the range queried by the user -(via fiemap->fm_length). +FIEMAP_EXTENT_LAST + This is generally the last extent in the file. A mapping attempt past + this extent may return nothing. Some implementations set this flag to + indicate this extent is the last one in the range queried by the user + (via fiemap->fm_length). + +FIEMAP_EXTENT_UNKNOWN + The location of this extent is currently unknown. This may indicate + the data is stored on an inaccessible volume or that no storage has + been allocated for the file yet. -* FIEMAP_EXTENT_UNKNOWN -The location of this extent is currently unknown. This may indicate -the data is stored on an inaccessible volume or that no storage has -been allocated for the file yet. +FIEMAP_EXTENT_DELALLOC + This will also set FIEMAP_EXTENT_UNKNOWN. -* FIEMAP_EXTENT_DELALLOC - - This will also set FIEMAP_EXTENT_UNKNOWN. -Delayed allocation - while there is data for this extent, its -physical location has not been allocated yet. + Delayed allocation - while there is data for this extent, its + physical location has not been allocated yet. -* FIEMAP_EXTENT_ENCODED -This extent does not consist of plain filesystem blocks but is -encoded (e.g. encrypted or compressed). Reading the data in this -extent via I/O to the block device will have undefined results. +FIEMAP_EXTENT_ENCODED + This extent does not consist of plain filesystem blocks but is + encoded (e.g. encrypted or compressed). Reading the data in this + extent via I/O to the block device will have undefined results. Note that it is *always* undefined to try to update the data in-place by writing to the indicated location without the @@ -145,32 +148,32 @@ unmounted, and then only if the FIEMAP_EXTENT_ENCODED flag is clear; user applications must not try reading or writing to the filesystem via the block device under any other circumstances. -* FIEMAP_EXTENT_DATA_ENCRYPTED - - This will also set FIEMAP_EXTENT_ENCODED -The data in this extent has been encrypted by the file system. +FIEMAP_EXTENT_DATA_ENCRYPTED + This will also set FIEMAP_EXTENT_ENCODED + The data in this extent has been encrypted by the file system. -* FIEMAP_EXTENT_NOT_ALIGNED -Extent offsets and length are not guaranteed to be block aligned. +FIEMAP_EXTENT_NOT_ALIGNED + Extent offsets and length are not guaranteed to be block aligned. -* FIEMAP_EXTENT_DATA_INLINE +FIEMAP_EXTENT_DATA_INLINE This will also set FIEMAP_EXTENT_NOT_ALIGNED -Data is located within a meta data block. + Data is located within a meta data block. -* FIEMAP_EXTENT_DATA_TAIL +FIEMAP_EXTENT_DATA_TAIL This will also set FIEMAP_EXTENT_NOT_ALIGNED -Data is packed into a block with data from other files. + Data is packed into a block with data from other files. -* FIEMAP_EXTENT_UNWRITTEN -Unwritten extent - the extent is allocated but its data has not been -initialized. This indicates the extent's data will be all zero if read -through the filesystem but the contents are undefined if read directly from -the device. +FIEMAP_EXTENT_UNWRITTEN + Unwritten extent - the extent is allocated but its data has not been + initialized. This indicates the extent's data will be all zero if read + through the filesystem but the contents are undefined if read directly from + the device. -* FIEMAP_EXTENT_MERGED -This will be set when a file does not support extents, i.e., it uses a block -based addressing scheme. Since returning an extent for each block back to -userspace would be highly inefficient, the kernel will try to merge most -adjacent blocks into 'extents'. +FIEMAP_EXTENT_MERGED + This will be set when a file does not support extents, i.e., it uses a block + based addressing scheme. Since returning an extent for each block back to + userspace would be highly inefficient, the kernel will try to merge most + adjacent blocks into 'extents'. VFS -> File System Implementation @@ -179,23 +182,23 @@ VFS -> File System Implementation File systems wishing to support fiemap must implement a ->fiemap callback on their inode_operations structure. The fs ->fiemap call is responsible for defining its set of supported fiemap flags, and calling a helper function on -each discovered extent: +each discovered extent:: -struct inode_operations { + struct inode_operations { ... int (*fiemap)(struct inode *, struct fiemap_extent_info *, u64 start, u64 len); ->fiemap is passed struct fiemap_extent_info which describes the -fiemap request: +fiemap request:: -struct fiemap_extent_info { + struct fiemap_extent_info { unsigned int fi_flags; /* Flags as passed from user */ unsigned int fi_extents_mapped; /* Number of mapped extents */ unsigned int fi_extents_max; /* Size of fiemap_extent array */ struct fiemap_extent *fi_extents_start; /* Start of fiemap_extent array */ -}; + }; It is intended that the file system should not need to access any of this structure directly. Filesystem handlers should be tolerant to signals and return @@ -203,9 +206,9 @@ EINTR once fatal signal received. Flag checking should be done at the beginning of the ->fiemap callback via the -fiemap_check_flags() helper: +fiemap_check_flags() helper:: -int fiemap_check_flags(struct fiemap_extent_info *fieinfo, u32 fs_flags); + int fiemap_check_flags(struct fiemap_extent_info *fieinfo, u32 fs_flags); The struct fieinfo should be passed in as received from ioctl_fiemap(). The set of fiemap flags which the fs understands should be passed via fs_flags. If @@ -216,10 +219,10 @@ ioctl_fiemap(). For each extent in the request range, the file system should call -the helper function, fiemap_fill_next_extent(): +the helper function, fiemap_fill_next_extent():: -int fiemap_fill_next_extent(struct fiemap_extent_info *info, u64 logical, - u64 phys, u64 len, u32 flags, u32 dev); + int fiemap_fill_next_extent(struct fiemap_extent_info *info, u64 logical, + u64 phys, u64 len, u32 flags, u32 dev); fiemap_fill_next_extent() will use the passed values to populate the next free extent in the fm_extents array. 'General' extent flags will diff --git a/Documentation/filesystems/index.rst b/Documentation/filesystems/index.rst index 815101241115..99b450260e4d 100644 --- a/Documentation/filesystems/index.rst +++ b/Documentation/filesystems/index.rst @@ -26,6 +26,7 @@ algorithms work. directory-locking devpts dnotify + fiemap automount-support |