On Thu, Aug 28, 2014 at 2:12 AM, Duncan <1i5t5.dun...@cox.net> wrote: > Holger Hoffstätte posted on Wed, 27 Aug 2014 23:33:55 +0000 as excerpted: > >> On Wed, 27 Aug 2014 15:58:49 -0700, G. Richard Bellamy wrote: >> >>> [..snip..] >> >> I can use fallocate on btrfs as you tried in your first post, with or >> without --keep-size, and it does the right things without errors. >> Running kernel 3.14+ (patched btrfs), util-linux-2.24.2 on Gentoo. >> >>> There are two things going wrong here. >>> >>> 1. The "open" command fallocate is using isn't passing along the >>> O_CREAT flag properly. >>> https://git.kernel.org/cgit/utils/util-linux/util-linux.git/tree/sys- >>> utils/fallocate.c#n368 > >>> CODE: fd = open(filename, O_RDWR | (!dig && !mode ? O_CREAT : 0), >>> 0644); >>> STRACE: open("test.test", O_RDWR) = -1 ENOENT (No such file or >>> directory) >> >> When you have fallocate.c open in cgit, go to its log and you will find >> a recent commit: >> >> https://git.kernel.org/cgit/utils/util-linux/util-linux.git/commit/sys- >> utils/fallocate.c?id=575718a04aa0c053875041dc387e360f2dcaa70d >> >> aka: "fallocate: use O_CREAT only for the default behavior" > > From the getopt_long processing switch/case while earlier in the file, > lines 319-321: > > case 'n': > mode |= FALLOC_FL_KEEP_SIZE; > break; > > > So mode is set to FALLOC_FL_KEEP_SIZE, the !mode test fails, and O_CREAT > isn't passed. > > Basically, you can't pass --keep-size/-n on a non-existent file; the file > doesn't exist so there's nothing to keep the size of and the fallocate > fails. Based on the commit, that's deliberate. > > So the no-existing-file behavior would seem to be NOTABUG.
The incantation I was using is from a bug report comment: https://bugzilla.redhat.com/show_bug.cgi?id=689127#c24 And yeah, I misread the !mode test, so the code is behaving as designed. My biggest crime, and wow what a doozy, is that I didn't read the frickin comment in the code. YOU KNOW, the one where it explains the new O_CREAT behavior? Those are hours I'm never going to get back, and it's because I, once again, wasn't paying attention. Now, whether you can pass --keep-size/-n on a non-existent file, you could in the past. > > > As for the existing-file case... > >>> And the strace of fallocate execution against a zero-length file I >>> created with touch: http://sprunge.us/BRML >>> >>> You can see in the strace that fallocate thinks it worked (= 0), >>> but here's the file post-execution: >>> 2014-08-27 15:49:45 root@eanna i ~ # ls -alh test.test >>> -rw------- 1 root root 0 Aug 27 15:46 test.test > > From the fallocate manpage: > -n, --keep-size > Do not modify the apparent length of the file. This may > effectively allocate blocks past EOF, which can be removed with a > truncate. > > Seems to me that's exactly what you're seeing -- allocation BEYOND EOF. > Try this: > > touch test.test > ls -lsh test.test > fallocate -n -l 1024000 test.test > ls -lsh test.test > > As described in the ls manpage, -s/--size displays the ALLOCATED size (as > opposed to the actual file size), and that *DOES* show the expected > ALLOCATED size change with util-linux-2.25 (and kernel 3.16) for me here, > tho the file size itself remains zero, as the fallocate manpage suggests > should indeed be the case if --keep-size was used. > > So it looks to me like it's working as it should. School is in again... and my goodness I learned a lot in this go-around. > >> Seems to me you need to downgrade util-linux and/or complain to the >> util-linux folks. In fact downgrade util-linux first (cfdisk in 2.25 >> eats partitions) and try fallocate again on whatever kernel you have >> running, just to rule out btrfs. > > On the eats partitions bit, gentoo bug: > > https://bugs.gentoo.org/show_bug.cgi?id=520838 > > Util-linux list thread on gmane, not much there but admitting the issue > and saying they plan a 2.25.1 ASAP: > > http://thread.gmane.org/gmane.linux.utilities.util-linux-ng/9765 > > > As a result, 2.25, which was in ~arch on gentoo, got hard-masked. Tho > I've standardized on gpt partitions and use gdisk (cgdisk) instead, so I > unmasked it again locally and kept it installed. I now use gdisk (cgdisk) when working with partitions - but in fact, did get bit by it recently. Duncan & Holger - I owe you both a beer! -rb -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
