xfs_bmap prints the map of disk blocks used by files in an XFS filesystem.
The map lists each <2>extent used by the file, as well as regions
in the file that do not have any corresponding blocks (<2>hole<1>s).
Each line of the listings takes the following form:
<2>extent<1><7>: [<1><2>startoffset<1><7>..<1><2>endoffset<1><7>]: c
<1><2>startblock<1><7>..<1><2>endblock<1>
Holes are marked by replacing the <2>startblock..endblock<1> with <2>hole.
All the file offsets and disk blocks are in units of 512-byte blocks,
no matter what the filesystem's block size is.
If portions of the file have been migrated offline by
a DMAPI application, a DMAPI read event will be generated to
bring those portions back online before the disk block map is
printed. However if the <3>-d<1> option is used, no DMAPI read event
will be generated for a DMAPI file and offline portions will be reported as holes.
If the <3>-l<1> option is used, then
<1><2><nblocks><1><7> <1><2>blocks<1><7>
will be appended to each line. <1><2>Nblocks<1><7> is the length
of the extent described on the line in units of 512-byte blocks.
If the <3>-a<1> option is given, information about the file's
attribute fork is printed instead of the default data fork.
If the <3>-n <2>nnn<1> option is given, <3>xfs_bmap<1> obtains the extent
list of the file in groups of <2>nnn<1> extents.
In the absence of <3>-n<1>, <3>xfs_bmap<1> queries the system for
the number of extents in the file and uses that value to compute
the group size.