Here is the copy from https://tools.ietf.org/html/rfc7530#page-40 Will Client query 'change' attribute every time before reading to know if the data has been changed? +-----------------+----+------------+-----+-------------------+ | Name | ID | Data Type | Acc | Defined in | +-----------------+----+------------+-----+-------------------+ | supported_attrs | 0 | bitmap4 | R | Section 5.8.1.1 | | type | 1 | nfs_ftype4 | R | Section 5.8.1.2 | | fh_expire_type | 2 | uint32_t | R | Section 5.8.1.3 | | change | 3 | changeid4 | R | Section 5.8.1.4 | | size | 4 | uint64_t | R W | Section 5.8.1.5 | | link_support | 5 | bool | R | Section 5.8.1.6 | | symlink_support | 6 | bool | R | Section 5.8.1.7 | | named_attr | 7 | bool | R | Section 5.8.1.8 | | fsid | 8 | fsid4 | R | Section 5.8.1.9 | | unique_handles | 9 | bool | R | Section 5.8.1.10 | | lease_time | 10 | nfs_lease4 | R | Section 5.8.1.11 | | rdattr_error | 11 | nfsstat4 | R | Section 5.8.1.12 | | filehandle | 19 | nfs_fh4 | R | Section 5.8.1.13 | +-----------------+----+------------+-----+-------------------+ On Thu, Feb 14, 2019 at 8:29 PM Jeff Layton <jlayton@xxxxxxxxxxxxxxx> wrote: > > On Thu, 2019-02-14 at 19:49 +0800, Marvin Zhang wrote: > > Hi Jeff, > > Another question is about Client Caching when disabling delegation. > > I set breakpoint on nfs4_op_read, which is OP_READ process function in > > nfs-ganesha. Then I read a file, I found that it will hit only once on > > the first time, which means latter reading operation on this file will > > not trigger OP_READ. It will read the data from client side cache. Is > > it right? > > Yes. In the absence of a delegation, the client will periodically query > for the inode attributes, and will serve reads from the cache if it > looks like the file hasn't changed. > > > I also checked the nfs client code in linux kernel. Only > > cache_validity is NFS_INO_INVALID_DATA, it will send OP_READ again, > > like this: > > if (nfsi->cache_validity & NFS_INO_INVALID_DATA) { > > ret = nfs_invalidate_mapping(inode, mapping); > > } > > This about this senario, client1 connect ganesha1 and client2 connect > > ganesha2. I read /1.txt on client1 and client1 will cache the data. > > Then I modify this file on client2. At that time, how client1 know the > > file is modifed and how it will add NFS_INO_INVALID_DATA into > > cache_validity? > > > Once you modify the code on client2, ganesha2 will request the necessary > caps from the ceph MDS, and client1 will have its caps revoked. It'll > then make the change. > > When client1 reads again it will issue a GETATTR against the file [1]. > ganesha1 will then request caps to do the getattr, which will end up > revoking ganesha2's caps. client1 will then see the change in attributes > (the change attribute and mtime, most likely) and will invalidate the > mapping, causing it do reissue a READ on the wire. > > [1]: There may be a window of time after you change the file on client2 > where client1 doesn't see it. That's due to the fact that inode > attributes on the client are only revalidated after a timeout. You may > want to read over the DATA AND METADATA COHERENCE section of nfs(5) to > make sure you understand how the NFS client validates its caches. > > Cheers, > -- > Jeff Layton <jlayton@xxxxxxxxxxxxxxx> > _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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