man/man8/xfs_io.8

.TH xfs_io 8
.SH NAME
xfs_io \- debug the I/O path of an XFS filesystem
.SH SYNOPSIS
.B xfs_io
[
.B \-adFfmrRstx
] [
.B \-c
.I cmd
] ... [
.B \-p
.I prog
]
.I file
.SH DESCRIPTION
.B xfs_io
is a debugging tool like
.BR 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).
.SH OPTIONS
.TP 1.0i
.BI \-c " cmd"
.B xfs_io
commands may be run interactively (the default) or as arguments on
the command line. Multiple
.B \-c
arguments may be given. The commands are run in the sequence given,
then the program exits.
.TP
.BI \-p " prog"
Set the program name for prompts and some error messages,
the default value is
.BR xfs_io .
.TP
.B \-F
Allow
.I file
to reside in non-XFS (foreign) filesystems.
This mode has a restricted set of commands.
.TP
.B \-f
Create
.I file
if it does not already exist.
.TP
.B \-r
Open
.I file
read-only, initially. This is required if
.I file
is immutable or append-only.
.TP
.B \-x
Expert mode. Dangerous commands are only available in this mode.
These commands also tend to require additional privileges.
.PP
The other
.BR open (2)
options described below are also available from the command line.
.SH CONCEPTS
.B 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.
.PP
.B 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.
.PP
The second set of commands exist for manipulating memory mapped regions
of a file - mapping, accessing, storing, unmapping, flushing, etc.
.PP
The remaining commands are for the navigation and display of data
structures relating to the open files, mappings, and the filesystems
where they reside.
.PP
Many commands have extensive online help. Use the
.B help
command for more details on any command.
.SH FILE I/O COMMANDS
.TP
.BI "file [ " N " ]"
Display a list of all open files and (optionally) switch to an alternate
current open file.
.TP
.BI "open [[ \-FacdfrstR ] " path " ]"
Closes the current file, and opens the file specified by
.I path
instead. Without any arguments, displays statistics about the current
file \- see the
.B stat
command.
.RS 1.0i
.PD 0
.TP 0.4i
.B \-F
allows non-XFS (foreign) files to be opened and
operated on with a restricted command set.
.TP
.B \-a
opens append-only (O_APPEND).
.TP
.B \-d
opens for direct I/O (O_DIRECT).
.TP
.B \-f
creates the file if it doesn't already exist (O_CREAT).
.TP
.B \-r
opens read-only (O_RDONLY).
.TP
.B \-s
opens for synchronous I/O (O_SYNC).
.TP
.B \-t
truncates on open (O_TRUNC).
.TP
.B \-R
marks the file as a realtime XFS file after
opening it, if it is not already marked as such.
.PD
.RE
.TP
.B o
See the
.B open
command.
.TP
.B close
Closes the current open file, marking the next open file as current
(if one exists).
.TP
.B c
See the
.B close
command.
.TP
.BI "pread [ \-b " bsize " ] [ \-v ] " "offset length"
Reads a range of bytes in a specified blocksize from the given
.IR offset .
.RS 1.0i
.PD 0
.TP 0.4i
.B \-b
can be used to set the blocksize into which the
.BR read (2)
requests will be split. The default blocksize is 4096 bytes.
.TP
.B \-v
dump the contents of the buffer after reading,
by default only the count of bytes actually read is dumped.
.PD
.RE
.TP
.B r
See the
.B pread
command.
.TP
.BI "pwrite [ \-i " file " ] [ \-d ] [ \-s " skip " ] [ \-b " size " ] [ \-S " seed " ] " "offset length"
Writes a range of bytes in a specified blocksize from the given
.IR offset .
The bytes written can be either a set pattern or read in from another
file before writing.
.RS 1.0i
.PD 0
.TP 0.4i
.B \-i
allows an input
.I file
to be specified as the source of the data to be written.
.TP
.B \-d
causes direct I/O, rather than the usual buffered
I/O, to be used when reading the input file.
.TP
.B \-s
specifies the number of bytes to
.I skip
from the start of the input file before starting to read.
.TP
.B \-b
used to set the blocksize into which the
.BR write (2)
requests will be split. The default blocksize is 4096 bytes.
.TP
.B \-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.
.RE
.PD
.TP
.B w
See the
.B pwrite
command.
.TP
.BI "bmap [ \-adlpv ] [ \-n " nx " ]"
Prints the block mapping for the current open file. Refer to the
.BR xfs_bmap (8)
manual page for complete documentation.
.TP
.BI "extsize [ \-R | \-D ] [ " value " ]"
Display and/or modify the preferred extent size used when allocating
space for the currently open file. If the
.B \-R
option is specified, a recursive descent is performed
for all directory entries below the currently open file
.RB ( \-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
.I 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.
.TP
.BI "allocsp " size " 0"
Sets the size of the file to
.I size
and zeroes any additional space allocated using the
XFS_IOC_ALLOCSP/XFS_IOC_FREESP system call described in the
.BR xfsctl (3)
manual page.
.B allocsp
and
.B freesp
do exactly the same thing.
.TP
.BI "freesp " size " 0"
See the
.B allocsp
command.
.TP
.BI "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).
.RS 1.0i
.PD 0
.TP 0.4i
.B \-d
the data will not be accessed again in the near future (POSIX_FADV_DONTNEED[*]).
.TP
.B \-n
data will be accessed once and not be reused (POSIX_FADV_NOREUSE[*]).
.TP
.B \-r
expect access to data in random order (POSIX_FADV_RANDOM), which sets readahead to zero.
.TP
.B \-s
expect access to data in sequential order (POSIX_FADV_SEQUENTIAL),
which doubles the default readahead on the file.
.TP
.B \-w
advises the specified data will be needed again (POSIX_FADV_WILLNEED[*])
which forces the maximum readahead.
.RE
.PD
.TP
.B fdatasync
Calls
.BR fdatasync (2)
to flush the file's in-core data to disk.
.TP
.B fsync
Calls
.BR fsync (2)
to flush all in-core file state to disk.
.TP
.B s
See the
.B fsync
command.
.TP
.BI resvsp " offset length"
Allocates reserved, unwritten space for part of a file using the
XFS_IOC_RESVSP system call described in the
.BR xfsctl (3)
manual page.
.TP
.BI unresvsp " offset length"
Frees reserved space for part of a file using the XFS_IOC_UNRESVSP
system call described in the
.BR xfsctl (3)
manual page.
.TP
.BI "falloc [ \-k ]" " offset length"
Allocates reserved, unwritten space for part of a file using the
fallocate routine as described in the
.BR fallocate (3)
manual page.
.RS 1.0i
.PD 0
.TP 0.4i
.B \-k
will set the FALLOC_FL_KEEP_SIZE flag as described in
.BR fallocate (3).
.PD
.RE
.TP
.BI truncate " offset"
Truncates the current file at the given offset using
.BR ftruncate (2).
.TP
.BI "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
.RB ( \-f )
or by path
.RB ( \-i ).

.SH MEMORY MAPPED I/O COMMANDS
.TP
.BI "mmap [ " N " | [[ \-rwx ] " "offset length " ]]
With no arguments,
.B mmap
shows the current mappings. Specifying a single numeric argument
.I N
sets the current mapping. If two arguments are specified (a range specified by
.I offset
and
.IR length ),
a new mapping is created spanning the range, and the protection mode can
be given as a combination of PROT_READ
.RB ( \-r ),
PROT_WRITE
.RB ( \-w ),
and PROT_EXEC
.RB ( \-x ).
.TP
.B mm
See the
.B mmap
command.
.TP
.B munmap
Unmaps the current memory mapping.
.TP
.B mu
See the
.B munmap
command.
.TP
.BI "mread [ \-f | \-v ] [ \-r ] [" " offset length " ]
Accesses a segment of the current memory mapping, optionally dumping it to
the standard output stream (with
.B \-v
or
.B \-f
option) for inspection. The accesses are performed sequentially from the start
.I offset
by default, but can also be done from the end backwards through the
mapping if the
.B \-r
option in specified.
The two verbose modes differ only in the relative offsets they display, the
.B \-f
option is relative to file start, whereas
.B \-v
shows offsets relative to the start of the mapping.
.TP
.B mr
See the
.B mread
command.
.TP
.BI "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
.B \-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
.B \-r
option in specified.
.TP
.B mw
See the
.B mwrite
command.
.TP
.BI "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
.RB ( \-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
.RB ( \-s)
or asynchronously
.RB ( \-a ).
.TP
.B ms
See the
.B msync
command.
.TP
.BI "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).
.RS 1.0i
.PD 0
.TP 0.4i
.B \-d
the pages will not be needed (POSIX_MADV_DONTNEED[*]).
.TP
.B \-r
expect random page references (POSIX_MADV_RANDOM), which sets readahead to zero.
.TP
.B \-s
expect sequential page references (POSIX_MADV_SEQUENTIAL),
which doubles the default readahead on the file.
.TP
.B \-w
advises the specified pages will be needed again (POSIX_MADV_WILLNEED[*])
which forces the maximum readahead.
.RE
.PD
.TP
.B mincore
Dumps a list of pages or ranges of pages that are currently in core,
for the current memory mapping.

.SH OTHER COMMANDS
.TP
.B print
Display a list of all open files and memory mapped regions.
The current file and current mapping are distinguishable from
any others.
.TP
.B p
See the
.B print
command.
.TP
.B quit
Exit
.BR xfs_io .
.TP
.B q
See the
.B quit
command.
.TP
.BR lsattr " [ " \-R " | " \-D " | " \-a " | " \-v " ]"
List extended inode flags on the currently open file. If the
.B \-R
option is specified, a recursive descent is performed
for all directory entries below the currently open file
.RB ( \-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.
.TP
.BR chattr " [ " \-R " | " \-D " ] [ " + / \-riasAdtPneEfS " ]"
Change extended inode flags on the currently open file. The
.B \-R
and
.B \-D
options have the same meaning as above. The mapping between each
letter and the inode flags (refer to
.BR xfsctl (3)
for the full list) is available via the
.B help
command.
.TP
.B freeze
Suspend all write I/O requests to the filesystem of the current file.
Only available in expert mode and requires privileges.
.TP
.B thaw
Undo the effects of a filesystem freeze operation.
Only available in expert mode and requires privileges.
.TP
.BI "inject [ " tag " ]"
Inject errors into a filesystem to observe filesystem behavior at
specific points under adverse conditions. Without the
.I tag
argument, displays the list of error tags available.
Only available in expert mode and requires privileges.
.TP
.BI "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.
.TP
.BR shutdown " [ " \-f " ]"
Force the filesystem to shutdown (with or without flushing the log).
Only available in expert mode and requires privileges.
.TP
.BR stat " [ " \-v " ]"
Selected statistics from
.BR stat (2)
and the XFS_IOC_GETXATTR system call on the current file. If the
.B \-v
option is specified, the atime (last access), mtime
(last modify), and ctime (last change) timestamps are also displayed.
.TP
.B statfs
Selected statistics from
.BR statfs (2)
and the XFS_IOC_FSGEOMETRY
system call on the filesystem where the current file resides.
.TP
.BR 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.
.RS 1.0i
.PD 0
.TP 0.4i
.B \-p
the output is similar to the default output except pathnames up to
the mount-point are printed out instead of the component name.
.TP
.B \-c
the file's filesystem will check all the parent attributes for consistency.
.TP
.B \-v
verbose output will be printed.
.RE
.IP
.B [NOTE: Not currently operational on Linux.]
.PD

.SH SEE ALSO
.BR mkfs.xfs (8),
.BR xfsctl (3),
.BR xfs_bmap (8),
.BR xfs_db (8),
.BR xfs (5),
.BR fdatasync (2),
.BR fstat (2),
.BR fstatfs (2),
.BR fsync (2),
.BR ftruncate (2),
.BR mmap (2),
.BR msync (2),
.BR open (2),
.BR pread (2),
.BR pwrite (2).