nfsd4: clean up downgrading code

In response to some review comments, get rid of the somewhat obscure
for-loop with bitops, and improve a comment.

Reported-by: Steve Dickson <steved@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

2 files changed, 27 insertions, 12 deletions

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index 8e253a347649..683885b18ceb 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -3523,16 +3523,29 @@ out:
         return status;
 }
 
-static inline void nfs4_file_downgrade(struct nfs4_ol_stateid *stp, unsigned int to_access)
+static inline void nfs4_stateid_downgrade_bit(struct nfs4_ol_stateid *stp, u32 access)
 {
-        int i;
+        if (!test_bit(access, &stp->st_access_bmap))
+                return;
+        nfs4_file_put_access(stp->st_file, nfs4_access_to_omode(access));
+        __clear_bit(access, &stp->st_access_bmap);
+}
 
-        for (i = 1; i < 4; i++) {
-                if (test_bit(i, &stp->st_access_bmap)
-                                        && ((i & to_access) != i)) {
-                        nfs4_file_put_access(stp->st_file, nfs4_access_to_omode(i));
-                        __clear_bit(i, &stp->st_access_bmap);
-                }
+static inline void nfs4_stateid_downgrade(struct nfs4_ol_stateid *stp, u32 to_access)
+{
+        switch (to_access) {
+        case NFS4_SHARE_ACCESS_READ:
+                nfs4_stateid_downgrade_bit(stp, NFS4_SHARE_ACCESS_WRITE);
+                nfs4_stateid_downgrade_bit(stp, NFS4_SHARE_ACCESS_BOTH);
+                break;
+        case NFS4_SHARE_ACCESS_WRITE:
+                nfs4_stateid_downgrade_bit(stp, NFS4_SHARE_ACCESS_READ);
+                nfs4_stateid_downgrade_bit(stp, NFS4_SHARE_ACCESS_BOTH);
+                break;
+        case NFS4_SHARE_ACCESS_BOTH:
+                break;
+        default:
+                BUG();
         }
 }
 
@@ -3578,7 +3591,7 @@ nfsd4_open_downgrade(struct svc_rqst *rqstp,
                         stp->st_deny_bmap, od->od_share_deny);
                 goto out;
         }
-        nfs4_file_downgrade(stp, od->od_share_access);
+        nfs4_stateid_downgrade(stp, od->od_share_access);
 
         reset_union_bmap_deny(od->od_share_deny, &stp->st_deny_bmap);
 
diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h
index 13f6f9f5ceec..22b065a55ea0 100644
--- a/fs/nfsd/state.h
+++ b/fs/nfsd/state.h
@@ -403,9 +403,11 @@ struct nfs4_file {
         /* One each for O_RDONLY, O_WRONLY, O_RDWR: */
         struct file *           fi_fds[3];
         /*
-         * Each open or lock stateid contributes 1 to either
-         * fi_access[O_RDONLY], fi_access[O_WRONLY], or both, depending
-         * on open or lock mode:
+         * Each open or lock stateid contributes 0-4 to the counts
+         * below depending on which bits are set in st_access_bitmap:
+         *     1 to fi_access[O_RDONLY] if NFS4_SHARE_ACCES_READ is set
+         *   + 1 to fi_access[O_WRONLY] if NFS4_SHARE_ACCESS_WRITE is set
+         *   + 1 to both of the above if NFS4_SHARE_ACCESS_BOTH is set.
          */
         atomic_t                fi_access[2];
         struct file             *fi_deleg_file;