On 2012-04-26, at 10:52, David Howells <dhowells@xxxxxxxxxx> wrote: > Steve French <smfrench@xxxxxxxxx> wrote: >> >> Both NFS and CIFS (and SMB2) can return inode numbers or equivalent unique >> identifier, but in the case of CIFS some old servers don't support the calls >> which return inode numbers (or don't return them for all file system types, >> Windows FAT?) so in these cases cifs has to create inode numbers on the fly >> on the client. inode numbers created on the client are not "stable" they can >> change on unmount/remount (which can cause problems for backup applications). > > In the volatile case you'd probably want to unset XSTAT_INO in st_mask as the > inode number is a local fabrication. I'd agree. Why fake up an inode number if the application doesn't care? Most apps don't actually use the inode. The only uses I know for the inode number in userspace are backup, CIFS/NFS servers, and "ls -li" . > However, since there is a remote file ID, > we could add an XSTAT_INFO_FILE_ID flag to indicate there's a standard xattr > holding this. It is a bit strange that the kernel would return a flag that was not requested, but not fatal. > On CIFS this could be the servername + pathname, on NFS this > could be the server address + FH on AFS the cell+volID+FID+uniquifier for > example. That's independent of xstat, however, and wouldn't be returned as > it's a blob that could be quite large. > > I presume in some cases, there is not a unique file ID that persists across > rename. > >> Similarly NFSv4 does not require that servers always return stable inode >> numbers (that will never change) and introduced a concept of "volatile file >> handle." > > Can I presume the inode number cannot be considered stable if the NFS4 FH is > non-volatile? Furthermore, can I presume NFS2/3 inode numbers are supposed to > be stable? > >> Basically the question is whether it is worth reporting a flag on the call >> which returns the inode number to indicate that the inode number is "stable" >> (would not change on reboot or reconnection) or "volatile." Since the >> majority of NFS and SMB2 servers can return stable inode numbers, I don't >> feel strongly about the need for an indicator of "stable" vs. "volatile" but >> I mention it because backup and migration applications mention this (if inode >> numbers are volatile, they may have to check for hardlinks differently for >> example) > > It may be that unsetting XSTAT_INO if you've fabricated the inode number > locally is sufficient. > >>>>> Handle remote filesystems being offline and indicate this with >>>>> XSTAT_INFO_OFFLINE. >>>> >>>> You already have support for an indicator for offline files (HSM), > > Which indicator is this? Or do you mean XSTAT_INFO_OFFLINE? > >>>> would XSTAT_INFO_OFFLINE be intended for the case >>>> where the network session to the server is disconnected >>>> (and in which you case the application does not want to reconnect)? >>> >>> Hmmm... Interesting question. Both NTFS and CIFS have an offline >>> attribute (which is where I originally got this from) - but should I have a >>> separate indicator to indicate the client can't access a server over a >>> network (ie. we've gone to disconnected operation on this file)? >>> E.g. should there be a XSTAT_INFO_DISCONNECTED too? >> >> my reaction is no, since it adds complexity. If you do a stat on a >> disconnected volume (where the network is temporarily down) reconnection will >> be attempted. If reconnection fails then the xstat will either fail or be >> retried forever depending on the value of "hard" vs. "soft" mount flag. > > I was thinking of how to handle disconnected operation, where you can't just > sit there and churn waiting for the server to come back or give an error. On > the other hand, as long as there's some spare space in the struct, we can deal > with that later when we actually start to implement D/O. > > David > -- > To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
