On 2012-04-26, at 10:52, David Howells dhowells@redhat.com wrote:
Steve French smfrench@gmail.com 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
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