On Mon, May 14, 2018 at 4:36 AM, Nikolay Borisov <nbori...@suse.com> wrote: > On 14.05.2018 11:20, Roman Mamedov wrote: >> On Mon, 14 May 2018 11:10:34 +0300 >> Nikolay Borisov <nbori...@suse.com> wrote: >> >>> But if we have mounted the fs with FORCE_COMPRESS shouldn't we disregard >>> the inode flags, presumably the admin knows what he is doing? >> >> Please don't. Personally I always assumed chattr +C would prevent both CoW >> and >> compression, and used that as a way to override volume-wide compress-force >> for >> a particular folder. Now that it turns out this wasn't working, the patch >> would fix it to behave in line with prior expectations. > > > So what made you have these expectation, is it codified somewhere > (docs/man pages etc)? I'm fine with that semantics IF this is what > people expect.
https://btrfs.wiki.kernel.org/index.php/Compression "Compression... does not work for NOCOW files." IMO, without a checksum, allowing compression is too much of a data risk. Uncompressed, user may be able to salvage most of the data with partial corruption. Compressed, they can't get anything to even look at, unless they have a mirrored copy that is fine, figure out which disk is corrupted, and mount degraded without it. > Now the question is why people grew up to have this expectation and not > the other way round? IMO force_compress should really disregard > everything else, if not then it should be documented. The man pages [0] > say: > > " > If compress-force is specified, the compression will allways be > attempted, but the data may end up uncompressed if the compression would > make them larger. > > As this is too simple, the compress-force is a workaround that will > compress most of the files at the cost of some wasted CPU cycles on > failed attempts. The heuristics of compress will improve in the future > so this will not be necessary. > " > > In this case I think the man page for this option should be documented > to say that inode-specific flags preclude mount flags. > > https://btrfs.wiki.kernel.org/index.php/Manpage/btrfs(5)#MOUNT_OPTIONS Agreed the man page should be clarified. -- 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
