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. |
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. | |
| |||||||||||||||||
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. | |||||||||||||||||
| |||||||||||||||||
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. | |||||||||||||||||
| |||||||||||||||||
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). | |||||||||||||||||
| |||||||||||||||||
fdatasync | Calls fdatasync(2) to flush the files 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. | |||||||||||||||||
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). | |||||||||
| |||||||||
mincore | Dumps a list of pages or ranges of pages that are currently in core,
for the current memory mapping.
| ||||||||
OTHER COMMANDS
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. | |||||||
| |||||||
[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).