xfs_io(1M)xfs_io(1M)NAMExfs_io - debug the I/O path of an XFS filesystem
SYNOPSISxfs_io [ -c cmd ] ... [ -p prog ] [ -adFfmrRstx ] file
DESCRIPTIONxfs_io is a debugging tool like xfs_db, but is aimed at examining the
regular file I/O path rather than the raw XFS volume itself.
The options to xfs_io are:
-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 Allow file to reside in non-XFS (foreign) filesystems. This
mode has a restricted set of commands.
-f Create file if it does not already exist.
-r Open file read-only, initially.
-x Expert mode. Dangerous commands are only available in this
mode. These commands also tend to require additional
privileges.
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 preallocation,
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.
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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 [ -FacdfrstR ] [ 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.
The -F option allows non-XFS (foreign) files to be opened and
operated on with a restricted command set.
The -a option opens append-only (O_APPEND).
The -d option opens for direct I/O (O_DIRECT).
The -f option creates the file if it doesn't already exist
(O_CREAT).
The -r option opens read-only (O_RDONLY).
The -s option opens for synchronous I/O (O_SYNC).
The -t option truncates on open (O_TRUNC).
The -R option 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 ]
Reads a range of bytes in a specified blocksize from the given
offset.
The -b option can be used to set the blocksize into which the
read(2) requests will be split. The default blocksize is 4096
bytes.
The -v option will dump the contents of the buffer after
reading, by default only the count of bytes actually read is
dumped.
r See the pread command.
pwrite [ -i file ] [ -d ] [ -s skip ] [ -b size ] [ -S seed ]
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.
The -i option allows an input file to be specified as the
source of the data to be written.
The -d option will cause direct I/O, rather than the usual
buffered I/O, to be used when reading the input file.
The -s options specifies the number of bytes to skip from the
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start of the input file before starting to read.
The -b option can be used to set the blocksize into which the
write(2) requests will be split. The default blocksize is 4096
bytes. The -S option is 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.
w See the pwrite command.
bmap [ -adlpv ] [ -n nx ]
Prints the block mapping for the current open file. Refer to
the xfs_bmap manual page for complete documentation.
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 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 offset length
Allocates zeroed space for part of a file using the
XFS_IOC_ALLOCSP system call described in the xfs manual page.
freesp offset length
Frees space for part of a file using the XFS_IOC_FREESP system
call described in the xfs manual page.
fadvise [ -dnrsw ]
On platforms which support it, allows hints be given to the
system regarding the expected I/O patterns on the file. The
hints are similar to those of the madvise command, discussed
later.
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.
resvsp offset length
Allocates reserved, unwritten space for part of a file using
the XFS_IOC_RESVSP system call described in the xfs manual
page.
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unresvsp offset length
Frees reserved space for part of a file using the
XFS_IOC_UNRESVSP system call described in the xfs manual page.
truncate offset
Truncates the current file at the given offset using
ftruncate(2).
sendfile -i infile | -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).
MEMORY MAPPED I/O COMMANDS
mmap [ -rwx ] [[ N ] | [ offset length ]]
With no arguments, mmap shows the current mappings. Specifying a
single numeric argument sets the current mapping. If two arguments
are specified (a range), 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 [ -frv ]
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 offsets relative
to the start of the mapping.
mr See the mread command.
mwrite [ -r ] [ -S seed ]
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.
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mw See the mwrite command.
msync
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 [ -drwsw ] [ 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). The -d option says the pages will not be
needed (POSIX_MADV_DONTNEED[*]). The -r option says to expect
random page references (POSIX_MADV_RANDOM), which sets readahead to
zero. The -s option says to expect sequential page references
(POSIX_MADV_SEQUENTIAL), which doubles the default readahead on the
file. The -w option 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 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 directories only). This is a depth first
descent, it does not follow symlinks and it also does not cross
mount points.
chattr [ -R | -D ] [ +/-riasAdtPn ]
Change extended inode flags on the currently open file. The -R and
-D options have the same meaning as above. The mapping between each
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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 an 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 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.
parent [ -cpv ]
By default this command prints out the parent inode numbers, inode
generation numbers and basenames of all the hardlinks which point to
the inode of the current file. If the -p option is specified, then
the output is similar to the default output except pathnames up to
the mount-point are printed out instead of the component name. If
the -c option is specified, then the file's filesystem will check
all the parent attributes for consistency. If the -v option is
specified, then verbose output will be printed. Not currently
operational on Linux.
IRIX SEE ALSOmkfs_xfs(1M), syssgi(2), xfs_bmap(1M), xfs_db(1M), xfs(4).
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xfs_io(1M)xfs_io(1M)LINUX SEE ALSOmkfs.xfs(8), xfsctl(3), xfs_bmap(8), xfs_db(8), xfs(5).
SEE ALSOfdatasync(2), fstat(2), fstatfs(2), fsync(2), ftruncate(2), mmap(2),
open(2), pread(2), pwrite(2).
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