/* Void Main's man pages */
{ phpMan } else { main(); }
xfs_io(8) xfs_io(8)
NAME
xfs_io - debug the I/O path of an XFS filesystem
SYNOPSIS
xfs_io [ -adFfmrRstx ] [ -c cmd ] ... [ -p prog ] file
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 argu-
ments 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. 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 addi-
tional privileges.
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 (option-
ally), 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, unmap-
ping, 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 [[ -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.
-F allows non-XFS (foreign) files to be opened and operated on with a restricted command set.
-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).
-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 ] 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.
r See the pread command.
pwrite [ -i file ] [ -d ] [ -s skip ] [ -b size ] [ -S seed ] 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.
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 documenta-
tion.
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 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 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_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 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.
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 fallo-
cate(3) manual page.
-k will set the FALLOC_FL_KEEP_SIZE flag as described in fallocate(3).
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).
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 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 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 offsets rela-
tive 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 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 reada-
head.
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 distinguish-
able 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. With-
out the tag argument, displays the list of error tags available. Only available in expert mode and requires priv-
ileges.
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.
-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).
xfs_io(8)
