Matija,
--On 31 October 2010 17:19:49 +0100 Matija Nalis <mnalis-ml@xxxxxxxxxx>
wrote:
Well, some metadata will have to be written, but not data.
shouldn't posix_fallocate(3) and/or fallocate(2) do that?
I haven't got EXT4 around ATM, but IIRC it should work on it too.
On XFS it seems to work too:
That's /almost/ perfect:
$ fallocate -l 1073741824 testfile
$ filefrag -v testfile
Filesystem type is: ef53
File size of testfile is 1073741824 (262144 blocks, blocksize 4096)
ext logical physical expected length flags
0 0 14819328 30720 unwritten
1 30720 14850048 30720 unwritten
2 61440 14880768 30720 unwritten
3 92160 14911488 30720 unwritten
4 122880 14942208 2048 unwritten
5 124928 14946304 14944255 30720 unwritten
6 155648 14977024 30720 unwritten
7 186368 15007744 30720 unwritten
8 217088 15038464 30720 unwritten
9 247808 15069184 14336 unwritten,eof
testfile: 2 extents found
I think all I need do is clear the unwritten flag in each of the extents.
Else I think if I read the file using ext4 later (i.e. after I've
written directly to the sectors concerned) it will appear to be
empty. Any idea how I do that?
--
Alex Bligh
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