Messages in this thread | | | Subject | Re: Problem: LTP linkat01 test fails on nfs directory (NFS v3) | From | Trond Myklebust <> | Date | Fri, 21 Sep 2007 08:37:07 -0400 |
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On Fri, 2007-09-21 at 13:13 +0400, Vitaliy Gusev wrote: > Hello. > > Tested kernels: 2.6.18, 2.6.22, 2.6.23-rc2 > > Steps to reproduce: Suppose that we have mounted some directory from nfs v3 > server with default options. Also we have the two directories in this > mountpoint and each directory has hard linked file. Try to open those files > and write to one and read from another. Data will not be equal. (Testcase: > attached hardlink_test.c)
Please retry after re-exporting the filesystem using the highly recommended "no_subtree_check" option. The default subtree_check option is broken: it changes the filehandle of the file upon a cross-directory rename() of that file.
> Analysis: Although these hard linked files have same nfs_fattr::fileid but > have different nfs_fh fhandle. In this case nfs_find_actor() function > (fs/nfs/inode.c) returns false during opening each file: > > nfs_find_actor() > { > ... > if (nfs_compare_fh(NFS_FH(inode), fh)) > return 0; > ... > } > > Therefore for each of hard links new struct inode is allocated. It leads to > cache aliasing. > > Please explain why nfs_find_actor() function compares file handles?
'cos this is the only way to know that two files are the same. fileid is not always supported by servers: it is an optional NFSv4 attribute, and on NFSv3, most non-posix filesystems will fake it using something like iunique().
Comparing filehandles allows you to be certain that two files are the same if the filehandles are equal. If they are not equal, then that does not guarantee that the files are different, but then how else are you going to determine it?
Trond
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