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xfs_io(8) - phpMan
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 obvi‐
ous 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 reg‐
ular file I/O - read, write, sync, space preallocation, etc.
The second set of commands exist for manipulating memory mapped regions of a file - map‐
ping, accessing, storing, unmapping, flushing, etc.
The remaining commands are for the navigation and display of data structures relating to
the open files, mappings, 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).
-s opens for synchronous I/O (O_SYNC).
-t truncates on open (O_TRUNC).
-n opens in non-blocking mode if possible (O_NONBLOCK).
-T create a temporary file not linked into the filesystem namespace (O_TMP‐
FILE). The pathname passed must refer to a directory which is treated as
virtual parent for the newly created invisible file. Can not be used
together with the -r option.
-R marks the file as a realtime XFS file after opening it, if it is not already
marked as such.
o See the open command.
close Closes the current open file, marking the next open file as current (if one
exists).
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 ] offset 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 writ‐
ten.
-d causes direct I/O, rather than the usual buffered I/O, to be used when read‐
ing 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 0xcdcd‐
cdcd.
-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 number 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 per‐
formed for all directory entries below the currently open file (-D can be used to
restrict the output to directories only). If the target file is a directory, then
the inherited extent size is set for that directory (new files created in that
directory inherit that extent size). The value should be specified in bytes, or
using one of the usual units suffixes (k, m, g, b, etc). The extent size is always
reported in units of bytes.
allocsp size 0
Sets the size of the file to size and zeroes any additional space allocated using
the XFS_IOC_ALLOCSP/XFS_IOC_FREESP system call described in the xfsctl(3) manual
page. allocsp and freesp do exactly the same thing.
freesp size 0
See the allocsp command.
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 argu‐
ments, the POSIX_FADV_NORMAL advice is implied (default readahead).
-d the data will not be accessed again in the near future (POSIX_FADV_DONT‐
NEED[*]).
-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 reada‐
head 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 maximum 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).
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.
fpunch offset length
Punches (de-allocates) blocks in the file by calling fallocate with the FAL‐
LOC_FL_PUNCH_HOLE flag as described in the fallocate(2) manual page.
fzero offset length
Call fallocate with FALLOC_FL_ZERO_RANGE flag as described in the fallocate(2) man‐
ual page to allocate and zero blocks within the range.
truncate offset
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, dis‐
play 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 speci‐
fied offset.
-s Display the starting lseek(2) offset. This offset will be a calcu‐
lated value when both data and holes are displayed together or per‐
forming a recusively display.
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 specified 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).
mm See the mmap command.
munmap Unmaps the current memory mapping.
mu See the munmap command.
mread [ -f | -v ] [ -r ] [ offset length ]
Accesses a segment of the current memory mapping, optionally dumping it to
the standard output stream (with -v or -f option) for inspection. The
accesses 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. The two verbose modes differ only in the relative offsets
they display, the -f option is relative to file start, whereas -v shows off‐
sets relative to the start of the mapping.
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 map‐
ping if no range specified) to their backing storage locations. Also,
optionally invalidates (-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 synchronously (-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 reada‐
head to zero.
-s expect sequential page references (POSIX_MADV_SEQUENTIAL), which dou‐
bles the default readahead on the file.
-w advises the specified pages will be needed again (POSIX_MADV_WILL‐
NEED[*]) which forces the maximum readahead.
mincore
Dumps a list of pages or ranges of pages that are currently in core, for the
current memory mapping.
OTHER 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
specified, a recursive descent is performed for all directory entries below
the currently open file (-D can be used to restrict the output to directo‐
ries only). This is a depth first descent, it does not follow symlinks and
it also does not cross mount points.
chattr [ -R | -D ] [ +/-riasAdtPneEfS ]
Change extended inode flags on the currently open file. The -R and -D
options have the same meaning as above. The mapping between each letter and
the inode flags (refer to xfsctl(3) for the full list) is available via the
help command.
freeze Suspend all write I/O requests to the filesystem of the current file. Only
available in expert mode and requires privileges.
thaw Undo the effects of a filesystem freeze operation. Only available in expert
mode and requires privileges.
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 privi‐
leges.
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
available in expert mode and requires privileges.
stat [ -v ]
Selected statistics from stat(2) and the XFS_IOC_GETXATTR system call on the
current 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 genera‐
tion numbers 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 con‐
sistency.
-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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