gfs2: Add GL_NOBLOCK flag

Add a GL_NOBLOCK flag for trying to take a glock without sleeping.  This
will be used for implementing non-blocking lookup (MAY_NOT_BLOCK in
gfs2_permission, LOOKUP_RCU in gfs2_drevalidate).

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>

diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
index d6bf1f8c25dcd19ecd62d3e819aa608126ae6ac3..2cb65f76eec88a040242d06394eb78e67dd077bf 100644 (file)
--- a/fs/gfs2/glock.c
+++ b/fs/gfs2/glock.c
@@ -516,6 +516,23 @@ static inline struct gfs2_holder *find_first_waiter(const struct gfs2_glock *gl)
        return NULL;
 }
 
+/**
+ * find_last_waiter - find the last gh that's waiting for the glock
+ * @gl: the glock
+ *
+ * This also is a fast way of finding out if there are any waiters.
+ */
+
+static inline struct gfs2_holder *find_last_waiter(const struct gfs2_glock *gl)
+{
+       struct gfs2_holder *gh;
+
+       if (list_empty(&gl->gl_holders))
+               return NULL;
+       gh = list_last_entry(&gl->gl_holders, struct gfs2_holder, gh_list);
+       return test_bit(HIF_HOLDER, &gh->gh_iflags) ? NULL : gh;
+}
+
 /**
  * state_change - record that the glock is now in a different state
  * @gl: the glock
@@ -1555,11 +1572,30 @@ trap_recursive:
 int gfs2_glock_nq(struct gfs2_holder *gh)
 {
        struct gfs2_glock *gl = gh->gh_gl;
-       int error = 0;
+       int error;
 
        if (glock_blocked_by_withdraw(gl) && !(gh->gh_flags & LM_FLAG_NOEXP))
                return -EIO;
 
+       if (gh->gh_flags & GL_NOBLOCK) {
+               struct gfs2_holder *current_gh;
+
+               error = -ECHILD;
+               spin_lock(&gl->gl_lockref.lock);
+               if (find_last_waiter(gl))
+                       goto unlock;
+               current_gh = find_first_holder(gl);
+               if (!may_grant(gl, current_gh, gh))
+                       goto unlock;
+               set_bit(HIF_HOLDER, &gh->gh_iflags);
+               list_add_tail(&gh->gh_list, &gl->gl_holders);
+               trace_gfs2_promote(gh);
+               error = 0;
+unlock:
+               spin_unlock(&gl->gl_lockref.lock);
+               return error;
+       }
+
        if (test_bit(GLF_LRU, &gl->gl_flags))
                gfs2_glock_remove_from_lru(gl);
 
@@ -1575,6 +1611,7 @@ int gfs2_glock_nq(struct gfs2_holder *gh)
        run_queue(gl, 1);
        spin_unlock(&gl->gl_lockref.lock);
 
+       error = 0;
        if (!(gh->gh_flags & GL_ASYNC))
                error = gfs2_glock_wait(gh);
 

diff --git a/fs/gfs2/glock.h b/fs/gfs2/glock.h
index 61197598abfd339c4e896e9909752a2abd9b31fc..0114f3e0ebe017b898ebb7aaa56e364f3792a7ed 100644 (file)
--- a/fs/gfs2/glock.h
+++ b/fs/gfs2/glock.h
@@ -84,6 +84,7 @@ enum {
 #define GL_SKIP                        0x0100
 #define GL_NOPID               0x0200
 #define GL_NOCACHE             0x0400
+#define GL_NOBLOCK             0x0800
   
 /*
  * lm_async_cb return flags