Ext4: Make file creation time, i_version and i_generation available by xattrs
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From: Andreas Dilger on 28 Jun 2010 15:10 On 2010-06-28, at 10:26, David Howells wrote: > Make the file creation time, inode data version number and inode generation > number available on Ext4 by as xattrs named: > > file.crtime > file.i_generation > file.i_version (directories only for ext4) Some minor nits: - I'd prefer calling these "file.generation" and "file.version". I don't think there is value in the "i_" prefix adds anything, and it seems more like an internal detail to me - why not expose the ".version" field for regular files? It seems that all of them are applicable for all file types. - it would be good to not introduce a new xattr namespace, since tools like tar (even the RHEL-patched one) will not backup and restore these namespaces. Using "trusted." would allow them to be backed up and restored using existing xattr-patched GNU tar by root, but wouldn't allow them to be modified by regular users. I think this is important for proper backup/restore of a filesystem, but can have correctness implications and shouldn't be accessible to regular users. > file.crtime=0x53ba244c000000000000000000000000 Is this a binary (host-endian) struct timespec? > file.i_generation=0x0000000000000000 This seems odd, i_generation should never be zero, AFAIK. Cheers, Andreas -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: David Howells on 28 Jun 2010 15:40 Andreas Dilger <adilger(a)dilger.ca> wrote: > - I'd prefer calling these "file.generation" and "file.version". > I don't think there is value in the "i_" prefix adds anything, > and it seems more like an internal detail to me That's reasonable. > - why not expose the ".version" field for regular files? It seems > that all of them are applicable for all file types. Because Ext4 doesn't support it for anything other than directories. > - it would be good to not introduce a new xattr namespace, since > tools like tar (even the RHEL-patched one) will not backup and > restore these namespaces. Using "trusted." would allow them to > be backed up and restored using existing xattr-patched GNU tar > by root, but wouldn't allow them to be modified by regular users. > I think this is important for proper backup/restore of a filesystem, > but can have correctness implications and shouldn't be accessible > to regular users. Does backing them up make sense, though? They are filesystem structural attributes. Can you restore the inode number, for example? If not, then you can't restore i_generation either. Restoring i_version might make sense, but what if it winds i_version backwards whilst maintaining i_ino and i_generation, that means there'll be a time in the future where the three values are once again what might have been already published - and may already be in someone's persistent cache. > > file.crtime=0x53ba244c000000000000000000000000 > > Is this a binary (host-endian) struct timespec? Yes. That might not be the best representation, however. It could also be, say "<decimal-secs>.<decimal-nsecs>", eg: "1234.000000567". > > file.i_generation=0x0000000000000000 > > This seems odd, i_generation should never be zero, AFAIK. That might be because it's the root directory, and so cannot be replaced. David -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: David Howells on 29 Jun 2010 18:50 Jeremy Allison <jra(a)samba.org> wrote: > We already have code in Samba to detect "birthtime" > (st_btime) as a returned member of a stat struct. Is it, though? Googling for st_btime suggests it could also be taken as the time last archived. That may just be a NetWareism though. David -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: David Howells on 29 Jun 2010 19:40
Jeremy Allison <jra(a)samba.org> wrote: > > Googling for st_btime suggests it could also be taken as the time last > > archived. That may just be a NetWareism though. > > It's a *BSD'ism. I meant that st_btime meaning "last archive time" may be a NetWareism. That seems to get more hits than anything else. David -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |