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nfsd: document open share bit tracking

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It's not immediately obvious from the code why we're doing this.

Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
Cc: Benny Halevy <bhalevy@panasas.com>
This commit is contained in:
J. Bruce Fields 2008-07-07 15:02:02 -04:00
parent 695e12f8d2
commit 4f83aa302f
1 changed files with 18 additions and 0 deletions
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18
fs/nfsd/nfs4state.c
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@ -1173,6 +1173,24 @@ static inline int deny_valid(u32 x)
return x <= NFS4_SHARE_DENY_BOTH;
}
/*
* We store the NONE, READ, WRITE, and BOTH bits separately in the
* st_{access,deny}_bmap field of the stateid, in order to track not
* only what share bits are currently in force, but also what
* combinations of share bits previous opens have used. This allows us
* to enforce the recommendation of rfc 3530 14.2.19 that the server
* return an error if the client attempt to downgrade to a combination
* of share bits not explicable by closing some of its previous opens.
*
* XXX: This enforcement is actually incomplete, since we don't keep
* track of access/deny bit combinations; so, e.g., we allow:
*
* OPEN allow read, deny write
* OPEN allow both, deny none
* DOWNGRADE allow read, deny none
*
* which we should reject.
*/
static void
set_access(unsigned int *access, unsigned long bmap) {
int i;