Request Basics
--------------
-A fiemap request is encoded within struct fiemap::
-
- struct fiemap {
- __u64 fm_start; /* logical offset (inclusive) at
- * which to start mapping (in) */
- __u64 fm_length; /* logical length of mapping which
- * userspace cares about (in) */
- __u32 fm_flags; /* FIEMAP_FLAG_* flags for request (in/out) */
- __u32 fm_mapped_extents; /* number of extents that were
- * mapped (out) */
- __u32 fm_extent_count; /* size of fm_extents array (in) */
- __u32 fm_reserved;
- struct fiemap_extent fm_extents[0]; /* array of mapped extents (out) */
- };
+A fiemap request is encoded within struct fiemap:
+.. kernel-doc:: include/uapi/linux/fiemap.h
+ :identifiers: fiemap
fm_start, and fm_length specify the logical range within the file
which the process would like mappings for. Extents returned mirror
If this flag is set, the extents returned will describe the inodes
extended attribute lookup tree, instead of its data tree.
+FIEMAP_FLAG_CACHE
+ This flag requests caching of the extents.
Extent Mapping
--------------
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:
+
+.. kernel-doc:: include/uapi/linux/fiemap.h
+ :identifiers: fiemap_extent
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
userspace would be highly inefficient, the kernel will try to merge most
adjacent blocks into 'extents'.
+FIEMAP_EXTENT_SHARED
+ This flag is set to request that space be shared with other files.
VFS -> File System Implementation
---------------------------------
u64 len);
->fiemap is passed struct fiemap_extent_info which describes the
-fiemap request::
-
- 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 */
- };
+fiemap request:
+
+.. kernel-doc:: include/linux/fiemap.h
+ :identifiers: fiemap_extent_info
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
#include <uapi/linux/fiemap.h>
#include <linux/fs.h>
+/**
+ * struct fiemap_extent_info - fiemap request to a filesystem
+ * @fi_flags: Flags as passed from user
+ * @fi_extents_mapped: Number of mapped extents
+ * @fi_extents_max: Size of fiemap_extent array
+ * @fi_extents_start: Start of fiemap_extent array
+ */
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 __user *fi_extents_start; /* Start of
- fiemap_extent array */
+ unsigned int fi_flags;
+ unsigned int fi_extents_mapped;
+ unsigned int fi_extents_max;
+ struct fiemap_extent __user *fi_extents_start;
};
int fiemap_prep(struct inode *inode, struct fiemap_extent_info *fieinfo,
#include <linux/types.h>
+/**
+ * struct fiemap_extent - description of one fiemap extent
+ * @fe_logical: byte offset of the extent in the file
+ * @fe_physical: byte offset of extent on disk
+ * @fe_length: length in bytes for this extent
+ * @fe_flags: FIEMAP_EXTENT_* flags for this extent
+ */
struct fiemap_extent {
- __u64 fe_logical; /* logical offset in bytes for the start of
- * the extent from the beginning of the file */
- __u64 fe_physical; /* physical offset in bytes for the start
- * of the extent from the beginning of the disk */
- __u64 fe_length; /* length in bytes for this extent */
+ __u64 fe_logical;
+ __u64 fe_physical;
+ __u64 fe_length;
+ /* private: */
__u64 fe_reserved64[2];
- __u32 fe_flags; /* FIEMAP_EXTENT_* flags for this extent */
+ /* public: */
+ __u32 fe_flags;
+ /* private: */
__u32 fe_reserved[3];
};
+/**
+ * struct fiemap - file extent mappings
+ * @fm_start: byte offset (inclusive) at which to start mapping (in)
+ * @fm_length: logical length of mapping which userspace wants (in)
+ * @fm_flags: FIEMAP_FLAG_* flags for request (in/out)
+ * @fm_mapped_extents: number of extents that were mapped (out)
+ * @fm_extent_count: size of fm_extents array (in)
+ * @fm_extents: array of mapped extents (out)
+ */
struct fiemap {
- __u64 fm_start; /* logical offset (inclusive) at
- * which to start mapping (in) */
- __u64 fm_length; /* logical length of mapping which
- * userspace wants (in) */
- __u32 fm_flags; /* FIEMAP_FLAG_* flags for request (in/out) */
- __u32 fm_mapped_extents;/* number of extents that were mapped (out) */
- __u32 fm_extent_count; /* size of fm_extents array (in) */
+ __u64 fm_start;
+ __u64 fm_length;
+ __u32 fm_flags;
+ __u32 fm_mapped_extents;
+ __u32 fm_extent_count;
+ /* private: */
__u32 fm_reserved;
- struct fiemap_extent fm_extents[]; /* array of mapped extents (out) */
+ /* public: */
+ struct fiemap_extent fm_extents[];
};
#define FIEMAP_MAX_OFFSET (~0ULL)
+/* flags used in fm_flags: */
#define FIEMAP_FLAG_SYNC 0x00000001 /* sync file data before map */
#define FIEMAP_FLAG_XATTR 0x00000002 /* map extended attribute tree */
#define FIEMAP_FLAG_CACHE 0x00000004 /* request caching of the extents */
#define FIEMAP_FLAGS_COMPAT (FIEMAP_FLAG_SYNC | FIEMAP_FLAG_XATTR)
+/* flags used in fe_flags: */
#define FIEMAP_EXTENT_LAST 0x00000001 /* Last extent in file. */
#define FIEMAP_EXTENT_UNKNOWN 0x00000002 /* Data location unknown. */
#define FIEMAP_EXTENT_DELALLOC 0x00000004 /* Location still pending.
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