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 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. 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.
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, 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 [[ -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 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 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
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.
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(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 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 offsets 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 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 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 ] [ +/-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 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)