xfs_io(8) System Manager's Manual xfs_io(8)
NAME
xfs_io - debug the I/O path of an XFS filesystem
SYNOPSIS
xfs_io [ -adfmrRstxT ] [ -c cmd ] ... [ -p prog ] file
xfs_io -V
DESCRIPTION
xfs_io is a debugging tool like xfs_db(8), but is aimed at examining the regular file I/O paths rather than
the raw XFS volume itself. These code paths include not only the obvious read/write/mmap interfaces for
manipulating files, but also cover all of the XFS extensions (such as space preallocation, additional inode
flags, etc).
OPTIONS
-c cmd xfs_io commands may be run interactively (the default) or as arguments on the command line. Multiple
-c arguments may be given. The commands are run in the sequence given, then the program exits.
-p prog Set the program name for prompts and some error messages, the default value is xfs_io.
-f Create file if it does not already exist.
-r Open file read-only, initially. This is required if file is immutable or append-only.
-x Expert mode. Dangerous commands are only available in this mode. These commands also tend to
require additional privileges.
-V Prints the version number and exits.
The other open(2) options described below are also available from the command line.
CONCEPTS
xfs_io maintains a number of open files and memory mappings. Files can be initially opened on the command
line (optionally), and additional files can also be opened later.
xfs_io commands can be broken up into three groups. Some commands are aimed at doing regular file I/O - read,
write, sync, space preallocation, etc.
The second set of commands exist for manipulating memory mapped regions of a file - mapping, accessing, stor‐
ing, unmapping, flushing, etc.
The remaining commands are for the navigation and display of data structures relating to the open files, map‐
pings, and the filesystems where they reside.
Many commands have extensive online help. Use the help command for more details on any command.
FILE I/O COMMANDS
file [ N ]
Display a list of all open files and (optionally) switch to an alternate current open file.
open [[ -acdfrstRT ] path ]
Closes the current file, and opens the file specified by path instead. Without any arguments, displays
statistics about the current file - see the stat command.
-a opens append-only (O_APPEND).
-d opens for direct I/O (O_DIRECT).
-f creates the file if it doesn't already exist (O_CREAT).
-r opens read-only (O_RDONLY).
c See the close command.
pread [ -b bsize ] [ -v ] [ -FBR [ -Z seed ] ] [ -V vectors ] offset length
Reads a range of bytes in a specified blocksize from the given offset.
-b can be used to set the blocksize into which the read(2) requests will be split. The default
blocksize is 4096 bytes.
-v dump the contents of the buffer after reading, by default only the count of bytes actually read
is dumped.
-F read the buffers in a forwards sequential direction.
-B read the buffers in a reserve sequential direction.
-R read the buffers in the give range in a random order.
-Z seed
specify the random number seed used for random reads.
-V vectors
Use the vectored IO read syscall preadv(2) with a number of blocksize length iovecs. The number
of iovecs is set by the vectors parameter.
r See the pread command.
pwrite [ -i file ] [ -d ] [ -s skip ] [ -b size ] [ -S seed ] [ -FBR [ -Z zeed ] ] [ -wW ] [ -V vectors ] off‐
set length
Writes a range of bytes in a specified blocksize from the given offset. The bytes written can be
either a set pattern or read in from another file before writing.
-i allows an input file to be specified as the source of the data to be written.
-d causes direct I/O, rather than the usual buffered I/O, to be used when reading the input file.
-s specifies the number of bytes to skip from the start of the input file before starting to read.
-b used to set the blocksize into which the write(2) requests will be split. The default blocksize
is 4096 bytes.
-S used to set the (repeated) fill pattern which is used when the data to write is not coming from
a file. The default buffer fill pattern value is 0xcdcdcdcd.
-F write the buffers in a forwards sequential direction.
-B write the buffers in a reserve sequential direction.
-R write the buffers in the give range in a random order.
-Z seed
specify the random number seed used for random write
-w call fdatasync(2) once all writes are complete (included in timing results)
-W call fsync(2) once all writes are complete (included in timing results)
-V vectors
Use the vectored IO write syscall pwritev(2) with a number of blocksize length iovecs. The num‐
ber of iovecs is set by the vectors parameter.
w See the pwrite command.
bmap [ -adlpv ] [ -n nx ]
Prints the block mapping for the current open file. Refer to the xfs_bmap(8) manual page for complete
documentation.
fiemap [ -alv ] [ -n nx ]
Prints the block mapping for the current open file using the fiemap ioctl. Options behave as described
in the xfs_bmap(8) manual page.
extsize [ -R | -D ] [ value ]
Display and/or modify the preferred extent size used when allocating space for the currently open file.
If the -R option is specified, a recursive descent is performed for all directory entries below the
fadvise [ -r | -s | [[ -d | -n | -w ] offset length ]]
On platforms which support it, allows hints be given to the system regarding the expected I/O patterns
on the file. The range arguments are required by some advise commands ([*] below), and the others must
have no range arguments. With no arguments, the POSIX_FADV_NORMAL advice is implied (default reada‐
head).
-d the data will not be accessed again in the near future (POSIX_FADV_DONTNEED[*]).
-n data will be accessed once and not be reused (POSIX_FADV_NOREUSE[*]).
-r expect access to data in random order (POSIX_FADV_RANDOM), which sets readahead to zero.
-s expect access to data in sequential order (POSIX_FADV_SEQUENTIAL), which doubles the default
readahead on the file.
-w advises the specified data will be needed again (POSIX_FADV_WILLNEED[*]) which forces the maxi‐
mum readahead.
fdatasync
Calls fdatasync(2) to flush the file's in-core data to disk.
fsync Calls fsync(2) to flush all in-core file state to disk.
s See the fsync command.
sync_range [ -a | -b | -w ] offset length
On platforms which support it, allows control of syncing a range of the file to disk. With no options,
SYNC_FILE_RANGE_WRITE is implied on the range supplied.
-a wait for IO in the given range to finish after writing (SYNC_FILE_RANGE_WAIT_AFTER).
-b wait for IO in the given range to finish before writing (SYNC_FILE_RANGE_WAIT_BEFORE).
-w start writeback of dirty data in the given range (SYNC_FILE_RANGE_WRITE).
sync Calls sync(2) to flush all filesystems' in-core data to disk.
syncfs Calls syncfs(2) to flush this filesystem's in-core data to disk.
resvsp offset length
Allocates reserved, unwritten space for part of a file using the XFS_IOC_RESVSP system call described
in the xfsctl(3) manual page.
unresvsp offset length
Frees reserved space for part of a file using the XFS_IOC_UNRESVSP system call described in the
xfsctl(3) manual page.
falloc [ -k ] offset length
Allocates reserved, unwritten space for part of a file using the fallocate routine as described in the
fallocate(2) manual page.
-k will set the FALLOC_FL_KEEP_SIZE flag as described in fallocate(2).
fcollapse offset length
Call fallocate with FALLOC_FL_COLLAPSE_RANGE flag as described in the fallocate(2) manual page to de-
allocates blocks and eliminates the hole created in this process by shifting data blocks into the hole.
finsert offset length
Call fallocate with FALLOC_FL_INSERT_RANGE flag as described in the fallocate(2) manual page to create
the hole by shifting data blocks.
fpunch offset length
Truncates the current file at the given offset using ftruncate(2).
sendfile -i srcfile | -f N [ offset length ]
On platforms which support it, allows a direct in-kernel copy between two file descriptors. The current
open file is the target, the source must be specified as another open file (-f) or by path (-i).
readdir [ -v ] [ -o offset ] [ -l length ]
Read a range of directory entries from a given offset of a directory.
-v verbose mode - dump dirent content as defined in readdir(3)
-o specify starting offset
-l specify total length to read (in bytes)
seek -a | -d | -h [ -r ] [ -s ] offset
On platforms that support the lseek(2) SEEK_DATA and SEEK_HOLE options, display the offsets of
the specified segments.
-a Display both data and hole segments starting at the specified offset.
-d Display the data segment starting at the specified offset.
-h Display the hole segment starting at the specified offset.
-r Recursively display all the specified segments starting at the specified offset.
-s Display the starting lseek(2) offset. This offset will be a calculated value when both
data and holes are displayed together or performing a recusively display.
reflink [ -C ] [ -q ] src_file [src_offset dst_offset length]
On filesystems that support the XFS_IOC_CLONE_RANGE or BTRFS_IOC_CLONE_RANGE ioctls, map
length bytes at offset dst_offset in the open file to the same physical blocks that are
mapped at offset src_offset in the file src_file , replacing any contents that may
already have been there. If a program writes into a reflinked block range of either
file, the dirty blocks will be cloned, written to, and remapped ("copy on write") in the
affected file, leaving the other file(s) unchanged. If src_offset, dst_offset, and
length are omitted, all contents of src_file will be reflinked into the open file.
-C Print timing statistics in a condensed format.
-q Do not print timing statistics at all.
dedupe [ -C ] [ -q ] src_file src_offset dst_offset length
On filesystems that support the XFS_IOC_FILE_EXTENT_SAME or
BTRFS_IOC_FILE_EXTENT_SAME ioctls, map length bytes at offset dst_offset in the
open file to the same physical blocks that are mapped at offset src_offset in the
file src_file , but only if the contents of both ranges are identical. This is
known as block-based deduplication. If a program writes into a reflinked block
range of either file, the dirty blocks will be cloned, written to, and remapped
("copy on write") in the affected file, leaving the other file(s) unchanged.
-C Print timing statistics in a condensed format.
-q Do not print timing statistics at all.
MEMORY MAPPED I/O COMMANDS
mmap [ N | [[ -rwx ] offset length ]]
With no arguments, mmap shows the current mappings. Specifying a single numeric
argument N sets the current mapping. If two arguments are specified (a range spec‐
ified by offset and length), a new mapping is created spanning the range, and the
protection mode can be given as a combination of PROT_READ (-r), PROT_WRITE (-w),
and PROT_EXEC (-x).
bose modes differ only in the relative offsets they display, the -f option is rel‐
ative to file start, whereas -v shows offsets relative to the start of the map‐
ping.
mr See the mread command.
mwrite [ -r ] [ -S seed ] [ offset length ]
Stores a byte into memory for a range within a mapping. The default stored value
is 'X', repeated to fill the range specified, but this can be changed using the -S
option. The memory stores are performed sequentially from the start offset by
default, but can also be done from the end backwards through the mapping if the -r
option in specified.
mw See the mwrite command.
msync [ -i ] [ -a | -s ] [ offset length ]
Writes all modified copies of pages over the specified range (or entire mapping if
no range specified) to their backing storage locations. Also, optionally invali‐
dates (-i) so that subsequent references to the pages will be obtained from their
backing storage locations (instead of cached copies). The flush can be done syn‐
chronously (-s) or asynchronously (-a).
ms See the msync command.
madvise [ -d | -r | -s | -w ] [ offset length ]
Modifies page cache behavior when operating on the current mapping. The range
arguments are required by some advise commands ([*] below). With no arguments,
the POSIX_MADV_NORMAL advice is implied (default readahead).
-d the pages will not be needed (POSIX_MADV_DONTNEED[*]).
-r expect random page references (POSIX_MADV_RANDOM), which sets readahead to
zero.
-s expect sequential page references (POSIX_MADV_SEQUENTIAL), which doubles
the default readahead on the file.
-w advises the specified pages will be needed again (POSIX_MADV_WILLNEED[*])
which forces the maximum readahead.
mincore
Dumps a list of pages or ranges of pages that are currently in core, for the cur‐
rent memory mapping.
OTHER COMMANDS
help [ command ]
Display a brief description of one or all commands.
print Display a list of all open files and memory mapped regions. The current file and
current mapping are distinguishable from any others.
p See the print command.
quit Exit xfs_io.
q See the quit command.
lsattr [ -R | -D | -a | -v ]
List extended inode flags on the currently open file. If the -R option is speci‐
fied, a recursive descent is performed for all directory entries below the cur‐
rently open file (-D can be used to restrict the output to directories only).
This is a depth first descent, it does not follow symlinks and it also does not
cross mount points.
flink path
Link the currently open file descriptor into the filesystem namespace.
inject [ tag ]
Inject errors into a filesystem to observe filesystem behavior at specific points
under adverse conditions. Without the tag argument, displays the list of error
tags available. Only available in expert mode and requires privileges.
resblks [ blocks ]
Get and/or set count of reserved filesystem blocks using the XFS_IOC_GET_RESBLKS
or XFS_IOC_SET_RESBLKS system calls. Note -- this can be useful for exercising
out of space behavior. Only available in expert mode and requires privileges.
shutdown [ -f ]
Force the filesystem to shutdown (with or without flushing the log). Only avail‐
able in expert mode and requires privileges.
stat [ -v ]
Selected statistics from stat(2) and the XFS_IOC_GETXATTR system call on the cur‐
rent file. If the -v option is specified, the atime (last access), mtime (last
modify), and ctime (last change) timestamps are also displayed.
statfs Selected statistics from statfs(2) and the XFS_IOC_FSGEOMETRY system call on the
filesystem where the current file resides.
chproj [ -R|-D ]
Modifies the project identifier associated with the current path. The -R option
will recursively descend if the current path is a directory. The -D option will
also recursively descend, only setting modifying projects on subdirectories. See
the xfs_quota(8) manual page for more information about project identifiers.
lsproj [ -R|-D ]
Displays the project identifier associated with the current path. The -R and -D
options behave as described above, in chproj.
parent [ -cpv ]
By default this command prints out the parent inode numbers, inode generation num‐
bers and basenames of all the hardlinks which point to the inode of the current
file.
-p the output is similar to the default output except pathnames up to the
mount-point are printed out instead of the component name.
-c the file's filesystem will check all the parent attributes for consistency.
-v verbose output will be printed.
[NOTE: Not currently operational on Linux.]
SEE ALSO
mkfs.xfs(8), xfsctl(3), xfs_bmap(8), xfs_db(8), xfs(5), fdatasync(2), fstat(2),
fstatfs(2), fsync(2), ftruncate(2), mmap(2), msync(2), open(2), pread(2), pwrite(2),
readdir(3).
xfs_io(8)
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