and I forgot to add… On 11/08/2021 12:36 am, Calum Mackay wrote:
hi Trond,I had a report that bash shell "truncate" redirection was not updating the mtime of a file, if that file already existed, and its size was already zero.That's trivial to reproduce, here on v5.14-rc3, NFSv4.1 mount: # date; > file1 Tue 10 Aug 14:41:08 PDT 2021 # ls -l file1 -rw-r--r-- 1 root root 0 Aug 10 14:41 file1 # date; > file1 Tue 10 Aug 14:43:06 PDT 2021 # ls -l file1 -rw-r--r-- 1 root root 0 Aug 10 14:41 file1An strace (of the second, above) shows that the bash shell is using open(O_TRUNC):10581 14:52:36.965048 open("file1", O_WRONLY|O_CREAT|O_TRUNC, 0666) = 3 <0.012124>and a pcap shows that the client is sending an OPEN(OPEN4_NOCREATE), then a CLOSE, but no SETATTR(size=0).I think this might be because of this optimisation, in the inode setattr op nfs_setattr():if (attr->ia_valid & ATTR_SIZE) { … if (attr->ia_size == i_size_read(inode)) attr->ia_valid &= ~ATTR_SIZE; } /* Optimization: if the end result is no change, don't RPC */if (((attr->ia_valid & NFS_VALID_ATTRS) & ~(ATTR_FILE|ATTR_OPEN)) == 0)return 0;and, indeed, there is no change here: the file already exists, and its size doesn't change.However, POSIX says, for open():If O_TRUNC is set and the file did previously exist, upon successful completion, open() shall mark for update the last data modification and last file status change timestamps of the file.[https://pubs.opengroup.org/onlinepubs/9699919799/functions/open.html] which suggest that this optimisation may not be valid, in this case.
This has been discussed before, way back in 2006: https://lore.kernel.org/linux-nfs/4485C3FE.5070504@xxxxxxxxxx/but in relation to SuSv43, where a similar clause did seem to include "if and only if the file size changes" which isn't in the POSIX IEEE Std 1003.1-2017 I quoted above.
So, I take it that this is still intentional? thanks, calum.
[there's a similar issue perhaps for ftruncate() where the size doesn't change]I haven't yet worked out whether in this case it's deliberate, but not POSIX compliant, or accidental.I'll continue looking, and come up with a patch if one is needed, but would appreciate any comments?thanks very much, cheers, calum.
-- Calum Mackay Linux Kernel Engineering Oracle Linux and Virtualisation
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