Commit 4f83aa30 authored by J. Bruce Fields's avatar J. Bruce Fields
Browse files

nfsd: document open share bit tracking 



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

Signed-off-by: default avatarJ. Bruce Fields <bfields@citi.umich.edu>
Cc: Benny Halevy <bhalevy@panasas.com>
parent 695e12f8

fs/nfsd/nfs4state.c

+18 −0
Original line number Diff line number Diff line
@@ -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;