ceph: enable/disable dentry complete flags via mount option

Enable/disable use of the dentry dir 'complete' flag via a mount option.
This lets the admin control whether ceph uses the dcache to satisfy
negative lookups or readdir when it has the entire directory contents in
its cache.

This is purely a performance optimization; correctness is guaranteed
whether it is enabled or not.

Reviewed-by: Christoph Hellwig <[e-mail]>
Signed-off-by: Sage Weil <[e-mail]>

Documentation/filesystems/ceph.txt

···
 	must rely on TCP's error correction to detect data corruption
 	in the data payload.
 
-  noasyncreaddir
-	Disable client's use its local cache to satisfy	readdir
-	requests.  (This does not change correctness; the client uses
-	cached metadata only when a lease or capability ensures it is
-	valid.)
+  dcache
+        Use the dcache contents to perform negative lookups and
+        readdir when the client has the entire directory contents in
+        its cache.  (This does not change correctness; the client uses
+        cached metadata only when a lease or capability ensures it is
+        valid.)
 
+  nodcache
+        Do not use the dcache as above.  This avoids a significant amount of
+        complex code, sacrificing performance without affecting correctness,
+        and is useful for tracking down bugs.
+
+  noasyncreaddir
+	Do not use the dcache as above for readdir.
 
 More Information
 ================

fs/ceph/dir.c

···
  */
 void ceph_dir_set_complete(struct inode *inode)
 {
-	/* not yet implemented */
+	struct dentry *dentry = d_find_any_alias(inode);
+	
+	if (dentry && ceph_dentry(dentry) &&
+	    ceph_test_mount_opt(ceph_sb_to_client(dentry->d_sb), DCACHE)) {
+		dout(" marking %p (%p) complete\n", inode, dentry);
+		set_bit(CEPH_D_COMPLETE, &ceph_dentry(dentry)->flags);
+	}
+	dput(dentry);
 }
 
 void ceph_dir_clear_complete(struct inode *inode)
 {
-	/* not yet implemented */
+	struct dentry *dentry = d_find_any_alias(inode);
+
+	if (dentry && ceph_dentry(dentry)) {
+		dout(" marking %p (%p) complete\n", inode, dentry);
+		set_bit(CEPH_D_COMPLETE, &ceph_dentry(dentry)->flags);
+	}
+	dput(dentry);
 }
 
 bool ceph_dir_test_complete(struct inode *inode)
 {
-	/* not yet implemented */
+	struct dentry *dentry = d_find_any_alias(inode);
+
+	if (dentry && ceph_dentry(dentry)) {
+		dout(" marking %p (%p) NOT complete\n", inode, dentry);
+		clear_bit(CEPH_D_COMPLETE, &ceph_dentry(dentry)->flags);
+	}
+	dput(dentry);
 	return false;
 }
 

fs/ceph/super.c

···
 	Opt_rbytes,
 	Opt_norbytes,
 	Opt_noasyncreaddir,
+	Opt_dcache,
+	Opt_nodcache,
 	Opt_ino32,
 };
 
···
 	{Opt_rbytes, "rbytes"},
 	{Opt_norbytes, "norbytes"},
 	{Opt_noasyncreaddir, "noasyncreaddir"},
+	{Opt_dcache, "dcache"},
+	{Opt_nodcache, "nodcache"},
 	{Opt_ino32, "ino32"},
 	{-1, NULL}
 };
···
 		break;
 	case Opt_noasyncreaddir:
 		fsopt->flags |= CEPH_MOUNT_OPT_NOASYNCREADDIR;
+		break;
+	case Opt_dcache:
+		fsopt->flags |= CEPH_MOUNT_OPT_DCACHE;
+		break;
+	case Opt_nodcache:
+		fsopt->flags &= ~CEPH_MOUNT_OPT_DCACHE;
 		break;
 	case Opt_ino32:
 		fsopt->flags |= CEPH_MOUNT_OPT_INO32;
···
 		seq_puts(m, ",norbytes");
 	if (fsopt->flags & CEPH_MOUNT_OPT_NOASYNCREADDIR)
 		seq_puts(m, ",noasyncreaddir");
+	if (fsopt->flags & CEPH_MOUNT_OPT_DCACHE)
+		seq_puts(m, ",dcache");
+	else
+		seq_puts(m, ",nodcache");
 
 	if (fsopt->wsize)
 		seq_printf(m, ",wsize=%d", fsopt->wsize);

fs/ceph/super.h

···
 #define CEPH_MOUNT_OPT_RBYTES          (1<<5) /* dir st_bytes = rbytes */
 #define CEPH_MOUNT_OPT_NOASYNCREADDIR  (1<<7) /* no dcache readdir */
 #define CEPH_MOUNT_OPT_INO32           (1<<8) /* 32 bit inos */
+#define CEPH_MOUNT_OPT_DCACHE          (1<<9) /* use dcache for readdir etc */
 
 #define CEPH_MOUNT_OPT_DEFAULT    (CEPH_MOUNT_OPT_RBYTES)