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Add xfs_io into xfsprogs, an xfs_db-alike program for the XFS IO path
which knows about direct IO, space preallocation, realtime files, etc
which the usual tools like dd don't unfortunately.  This is a fixed-up
version of a hacked tool that I found useful for coding, debugging and
testing unwritten extents; hopefully it'll be useful for realtime too.

.TH xfs_io 8
.SH NAME
xfs_io \- debug the IO path of an XFS filesystem
.SH SYNOPSIS
.nf
\f3xfs_io\f1 [ \f3\-c\f1 cmd ] ... [ \f3\-p\f1 prog ] [ \f3\-r\f1 ] file
.fi
.SH DESCRIPTION
\f2xfs_io\f1 is a debugging tool like \f2xfs_db\f1(8), but is aimed
at examining the regular file IO path rather than the raw XFS volume
itself.
.PP
The options to \f2xfs_io\f1 are:
.TP 10
\f3\-c\f1 \f2cmd\f1
\f2xfs_io\f1 commands may be run interactively (the default)
or as arguments on the command line.
Multiple \f3\-c\f1 arguments may be given.
The commands are run in the sequence given, then the program exits.
This is the mechanism used to implement \f2xfs_bmap\f1(8).
.TP
\f3\-p\f1 \f2prog\f1
Set the program name for prompts and some error messages,
the default value is \f2xfs_io\f1.
.TP
\f3\-r\f1
Open \f2file\f1 read-only, initially.
.SH CONCEPTS
\f2xfs_io\f1 always maintains one current open file in the filesystem.
This is initially specified on the command line, but alternate files
can be specified later (one at a time \- see the ``open'' command).
.PP
\f2xfs_io\f1 commands can be broken up into two distinct classes.
Most commands are for doing IO to the file in some way - reads, writes,
or space preallocation.
Other commands are for the navigation and display of data structures
relating to the open file or the filesystem it resides in.
.SH COMMANDS
.PP
Many commands have extensive online help.
Use the \f3help\f1 command for more details on any command.
.TP 10
\f3allocsp\f1 \f2offset\f1 \f2length\f1
Allocates zeroed space for part of a file using the XFS_IOC_ALLOCSP
system call described in \f2xfs\f1(5).
.TP
\f3freesp\f1 \f2offset\f1 \f2length\f1
Frees space for part of a file using the XFS_IOC_FREESP
system call described in \f2xfs\f1(5).
.TP
\f3bmap\f1 [ \f2-adlpv\f1 ] [ \f2-n nx\f1 ]
Prints the block mapping for the open file.
Refer to \f2xfs_bmap\f1(8) for complete documentation.
.TP
\f3fdatasync\f1
Calls \f2fdatasync\f1(2) to flush the open file's in-core data to disk.
.TP
\f3fsync\f1
Calls \f2fsync\f1(2) to flush all in-core file state to disk.
.TP
\f3o\f1
See the \f3open\f1 command.
.TP
\f3open\f1 [ \f2-acdrstx\f1 ] [ \f2path\f1 ]
Closes the current file, and opens the file specified by \f2path\f1 instead.
Without any arguments, displays statistics about the currently open file \-
see the \f3stat\f1 command.
.br
The \f3\-a\f1 option opens append-only (O_APPEND).
.br
The \f3\-c\f1 option creates the file if it doesn't already exist (O_CREAT).
.br
The \f3\-d\f1 option opens for direct IO (O_DIRECT).
.br
The \f3\-r\f1 option opens read-only (O_RDONLY).
.br
The \f3\-s\f1 option opens for synchronous IO (O_SYNC).
.br
The \f3\-t\f1 option truncates on open (O_TRUNC).
.br
The \f3\-x\f1 option marks the file as a realtime XFS file after
opening it, if it is not already marked as such.
.TP
\f3pread\f1
Reads a range of bytes in a specified blocksize from the given offset.
.br
The \f3\-b\f1 option can be used to set the blocksize into which the
\f2read\f1(2) requests will be split.
The default blocksize is 4096 bytes.
.br
The \f3\-v\f1 option will dump the contents of the buffer after reading,
by default only the count of bytes actually read is dumped.
.TP
\f3pwrite\f1
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.
.br
The \f3\-i\f1 option allows an input file to be specified as the source
of the data to be written.
.br
The \f3\-d\f1 option will cause direct IO, rather than the usual buffered
IO, to be used when reading the input file.
.br
The \f3\-s\f1 options specifies the number of bytes to skip from the
start of the input file before starting to read.
.br
The \f3\-b\f1 option can be used to set the blocksize into which the
\f2read\f1(2) requests will be split.
The default blocksize is 4096 bytes.
The \f3\-S\f1 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.
.TP
\f3q\f1
See the \f3quit\f1 command.
.TP
\f3quit\f1
Exit \f2xfs_io\f1.
.TP
\f3r\f1
See the \f3pread\f1 command.
.TP
\f3resblks\f1 [ \f2blocks\f1 ]
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 \f2xfs\f1(5).
Note \-\- this can be useful for exercising out of space behavior.
.TP
\f3resvsp\f1 \f2offset\f1 \f2length\f1
Allocates reserved, unwritten space for part of a file using the XFS_IOC_RESVSP
system call described in \f2xfs\f1(5).
.TP
\f3unresvsp\f1 \f2offset\f1 \f2length\f1
Frees reserved space for part of a file using the XFS_IOC_UNRESVSP
system call described in \f2xfs\f1(5).
.TP
\f3s\f1
See the \f3fsync\f1 command.
.TP
\f3stat\f1 [ \f2-v\f1 ]
Selected statistics from \f2stat\f1(2) and the XFS_IOC_GETXATTR
system call from \f2xfs\f1(5) on the currently open file.
If the \f2-v\f1 option is specified, the atime (last access), mtime
(last modify), and ctime (last change) timestamps are also displayed.
.TP
\f3statfs\f1
Selected statistics from \f2statfs\f1(2) and the XFS_IOC_FSGEOMETRY
system call from \f2xfs\f1(5) on the filesystem where the currently
open file resides.
.TP
\f3truncate\f1 \f2offset\f1
Truncates the current file at the given offset using \f2ftruncate\f1(2).
.TP
\f3w\f1
See the \f3pwrite\f1 command.
.SH SEE ALSO
fdatasync(2),
fstat(2),
fstatfs(2),
fsync(2),
ftruncate(2),
mkfs.xfs(8),
open(2),
pread(2),
pwrite(2),
xfs_bmap(8),
xfs_db(8),
xfs(5).