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).