xfs_io(8)xfs_io(8)NAMExfs_io - debug the I/O path of an XFS filesystem
SYNOPSISxfs_io [ -adfmrRstx ] [ -c cmd ] ... [ -p prog ] file
xfs_io-V
DESCRIPTIONxfs_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 inter‐
faces 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 privi‐
leges.
-V Prints the version number and exits.
The other open(2) options described below are also available from the
command line.
CONCEPTSxfs_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 prealloca‐
tion, etc.
The second set of commands exist for manipulating memory mapped regions
of a file - mapping, 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 [[ -acdfrstR ] 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).
-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 cur‐
rent (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 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 num‐
ber 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 allo‐
cating space for 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 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 sys‐
tem 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 readahead).
-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_RAN‐
DOM), which sets readahead to zero.
-s expect access to data in sequential order
(POSIX_FADV_SEQUENTIAL), which doubles the default reada‐
head on the file.
-w advises the specified data will be needed again
(POSIX_FADV_WILLNEED[*]) which forces the maximum reada‐
head.
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).
fpunch offset length
Punches (de-allocates) blocks in the file by calling fallocate
with the FALLOC_FL_PUNCH_HOLE flag as described in the fallo‐
cate(2) manual page.
truncate offset
Truncates the current file at the given offset using ftrun‐
cate(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 tar‐
get, 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 read‐
dir(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 recu‐
sively display.
MEMORY MAPPED I/O COMMANDS
mmap [ N | [[ -rwx ] offset length ]]
With no arguments, mmap shows the current mappings. Spec‐
ifying a single numeric argument N sets the current map‐
ping. 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 com‐
bination 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, option‐
ally 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 mapping 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 cur‐
rent 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_DONT‐
NEED[*]).
-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 cur‐
rently 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 dis‐
tinguishable 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 per‐
formed 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.
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 flush‐
ing 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_FSGE‐
OMETRY system call on the filesystem where the current
file resides.
chproj [ -R|-D ]
Modifies the project identifier associated with the cur‐
rent 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 cur‐
rent path. The -R and -D options behave as described
above, in chproj.
parent [ -cpv ]
By default this command prints out the parent inode num‐
bers, inode generation 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 consistency.
-v verbose output will be printed.
[NOTE: Not currently operational on Linux.]
SEE ALSOmkfs.xfs(8), xfsctl(3), xfs_bmap(8), xfs_db(8), xfs(5), fdata‐
sync(2), fstat(2), fstatfs(2), fsync(2), ftruncate(2), mmap(2),
msync(2), open(2), pread(2), pwrite(2), readdir(3).
xfs_io(8)
