Hello,
I've been trying lately to develop a solution for the problem with
open() that manifests itself in ESTALE error in the following situation:
1. NFS server: echo "1111" > file01
2. NFS client: cat file01
3. NFS server: echo "2222" > file02 && mv file02 file01
4. NFS client: cat file01 (either old file01 contents or ESTALE)
My study shows that actually the problem appears to be in VOP_ACCESS()
which is called from vn_open(). If nfs_access() decides to "go to the wire"
in #4, it then uses a cached file handle which is indeed stale. Thus,
open() eventually fails with ESTALE too (ESTALE comes from underlying
nfs_request()).
I understand all the fundamental NFS-related integrity problems, but not
this one :) That is, I see no reason for open() to fail to open a file for
reading or writing if the system knows the problem is it's own. Why not
just do another lookup and try obtain a valid file handle?
I was playing with different parts of the kernel while "fixing" this for
myself. However, I believe, the simpliest patch would be for
vfs_syscalls.c:open() (I've also made a working patch against vn_open(),
though).
Could anyone please be so kind to comment this issue?
TIA
--- kern/vfs_syscalls.c.orig Thu Jun 19 13:22:50 2003
+++ kern/vfs_syscalls.c Thu Jun 19 13:29:11 2003
@@ -1008,6 +1008,7 @@
int type, indx, error;
struct flock lf;
struct nameidata nd;
+ int stale = 0;
oflags = SCARG(uap, flags);
if ((oflags & O_ACCMODE) == O_ACCMODE)
@@ -1025,8 +1026,15 @@
* the descriptor while we are blocked in vn_open()
*/
fhold(fp);
+again:
error = vn_open(&nd, flags, cmode);
if (error) {
+ /*
+ * if the underlying filesystem returns ESTALE
+ * we must have used a cached file handle.
+ */
+ if (error == ESTALE && stale++ == 0)
+ goto again;
/*
* release our own reference
*/
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