xfs_io(8)

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

SYNOPSIS
xfs_io [ -c cmd ] ... [ -p prog ] [ -adFfmrRstx ] file

DESCRIPTION
xfs_io is a debugging tool like xfs_db(8), but is aimed at examining the regular file I/O path rather than the raw XFS volume itself.

The options to xfs_io are:

-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.

-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.
    The -F option allows non-XFS (foreign) files to be opened and operated on with a restricted command set.
    The -a option opens append-only (O_APPEND).
    The -d option opens for direct I/O (O_DIRECT).
    The -f option creates the file if it doesn't already exist (O_CREAT).
    The -r option opens read-only (O_RDONLY).
    The -s option opens for synchronous I/O (O_SYNC).
    The -t option truncates on open (O_TRUNC).
    The -R option 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 ]
    Reads a range of bytes in a specified blocksize from the given offset.
    The -b option can be used to set the blocksize into which the read(2) requests will be split. The default blocksize is 4096 bytes.
    The -v option will 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 ]
    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.
    The -i option allows an input file to be specified as the source of the data to be written.
    The -d option will cause direct I/O, rather than the usual buffered I/O, to be used when reading the input file.
    The -s options specifies the number of bytes to skip from the start of the input file before starting to read.
    The -b option can be used to set the blocksize into which the write(2) requests will be split. The default blocksize is 4096 bytes. The -S option is 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 xfs_bmap(8) for complete documentation.

allocsp offset length
    Allocates zeroed space for part of a file using the XFS_IOC_ALLOCSP system call described in xfs(5).

freesp offset length
    Frees space for part of a file using the XFS_IOC_FREESP system call described in xfs(5).

fadvise [ -dnrsw ]
    On platforms which support it, allows hints be given to the system regarding the expected I/O patterns on the file. The hints are similar to those of the madvise command, discussed later.

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 xfs(5).

unresvsp offset length
    Frees reserved space for part of a file using the XFS_IOC_UNRESVSP system call described in xfs(5).

truncate offset
    Truncates the current file at the given offset using ftruncate(2).

sendfile -i infile | -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 [ -rwx ] [[ N ] | [ offset length ]]
    With no arguments, mmap shows the current mappings. Specifying a single numeric argument sets the current mapping. If two arguments are specified (a range), 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 [ -frv ]
    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 ]
    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
    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 [ -drwsw ] [ 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). The -d option says the pages will not be needed (POSIX_MADV_DONTNEED[*]). The -r option says to expect random page references (POSIX_MADV_RANDOM), which sets readahead to zero. The -s option says to expect sequential page references (POSIX_MADV_SEQUENTIAL), which doubles the default readahead on the file. The -w option 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 ] [ +/-riasAdtPn ]
    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 an 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, as described in xfs(5). 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 from xfs(5) 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 from xfs(5) on the filesystem where the current file resides.

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