[PATCH 19/21] staging: lustre: fid: fix up debugfs access to ->lcs_space

[NeilBrown]

lcs_space can change while the lock is not held
if an RPC in underway.  This can be detected by
seq->ls_update being set.

In this case, reading or writing the value should return
-EBUSY.

Also, the D_INFO CDEBUG() which reports the lcs_space being
updated never fires, as it tests the wrong value -
ldebugfs_fid_write_common() returns 'count' on success.

Finally, this return value should be returned from
ldebugfs_fid_space_seq_write(), rather than always returning 'count',
so that errors can be detected.

Signed-off-by: NeilBrown <ne...@suse.com>
---
 drivers/staging/lustre/lustre/fid/lproc_fid.c |   15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/drivers/staging/lustre/lustre/fid/lproc_fid.c 
b/drivers/staging/lustre/lustre/fid/lproc_fid.c
index e05487662afd..a1e5bf9f36ec 100644
--- a/drivers/staging/lustre/lustre/fid/lproc_fid.c
+++ b/drivers/staging/lustre/lustre/fid/lproc_fid.c
@@ -106,28 +106,35 @@ ldebugfs_fid_space_seq_write(struct file *file,
        rc = ldebugfs_fid_write_common(buffer, count, &range);
 
        spin_lock(&seq->lcs_lock);
+       if (seq->lcs_update)
+               /* An RPC call is active to update lcs_space */
+               rc = -EBUSY;
        if (rc > 0)
                seq->lcs_space = range;
        spin_unlock(&seq->lcs_lock);
 
-       if (rc == 0) {
+       if (rc > 0) {
                CDEBUG(D_INFO, "%s: Space: " DRANGE "\n",
                       seq->lcs_name, PRANGE(&range));
        }
 
-       return count;
+       return rc;
 }
 
 static int
 ldebugfs_fid_space_seq_show(struct seq_file *m, void *unused)
 {
        struct lu_client_seq *seq = (struct lu_client_seq *)m->private;
+       int rc = 0;
 
        spin_lock(&seq->lcs_lock);
-       seq_printf(m, "[%#llx - %#llx]:%x:%s\n", PRANGE(&seq->lcs_space));
+       if (seq->lcs_update)
+               rc = -EBUSY;
+       else
+               seq_printf(m, "[%#llx - %#llx]:%x:%s\n", 
PRANGE(&seq->lcs_space));
        spin_unlock(&seq->lcs_lock);
 
-       return 0;
+       return rc;
 }
 
 static ssize_t