xfs_io(8)

NAME
xfs_io - debug the I/O path of an XFS filesystem

SYNOPSIS
xfs_io [ -adfmrRstx ] [ -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  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 [[ -acdfrstR ] 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.
    -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 ] [ -FBR [ -Z seed ] ] [ -V vectors ] 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.
    -F  read the buffers in a forwards sequential direction.
    -B  read the buffers in a reserve sequential direction.
    -R  read the buffers in the give range in a random order.
    -Z seed
        specify the random number seed used for random reads.
    -V vectors
        Use the vectored IO read syscall preadv(2) with a number of blocksize length iovecs. The number of iovecs is set by the vectors parameter.

r   See the pread command.

pwrite [ -i file ] [ -d ] [ -s skip ] [ -b size ] [ -S seed ] [ -FBR [ -Z zeed ] ] [ -wW ] [ -V vectors ] 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.
    -F  write the buffers in a forwards sequential direction.
    -B  write the buffers in a reserve sequential direction.
    -R  write the buffers in the give range in a random order.
    -Z seed
        specify the random number seed used for random write
    -w  call fdatasync(2) once all writes are complete (included in timing results)
    -W  call fsync(2) once all writes are complete (included in timing results)
    -V vectors
        Use the vectored IO write syscall pwritev(2) with a number of blocksize length iovecs. The number of iovecs is set by the vectors parameter.

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.

sync_range [ -a | -b | -w ] offset length
    On platforms which support it, allows control of syncing a range of the file to disk. With no options, SYNC_FILE_RANGE_WRITE is implied on the range supplied.
    -a  wait for IO in the given range to finish after writing (SYNC_FILE_RANGE_WAIT_AFTER).
    -b  wait for IO in the given range to finish before writing (SYNC_FILE_RANGE_WAIT_BEFORE).
    -w  start writeback of dirty data in the given range (SYNC_FILE_RANGE_WRITE).

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).