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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)