[PATCH] open_by_devnum()

	New helper - open_by_devnum().  Opens block_device by device number;
for use in situations when we really have nothing better than dev_t (i.e.
had received it from stupid userland API).

drivers/md/dm-table.c

@@ -345,26 +345,21 @@ static struct dm_dev *find_device(struct list_head *l, dev_t dev)
 static int open_dev(struct dm_dev *d, dev_t dev)
 {
 	static char *_claim_ptr = "I belong to device-mapper";
+	struct block_device *bdev;
 
 	int r;
 
 	if (d->bdev)
 		BUG();
 
-	d->bdev = bdget(dev);
-	if (!d->bdev)
-		return -ENOMEM;
-
-	r = blkdev_get(d->bdev, d->mode, 0, BDEV_RAW);
+	bdev = open_by_devnum(dev, d->mode, BDEV_RAW);
+	if (IS_ERR(bdev))
+		return PTR_ERR(bdev);
+	r = bd_claim(bdev, _claim_ptr);
 	if (r)
-		return r;
-
-	r = bd_claim(d->bdev, _claim_ptr);
-	if (r) {
-		blkdev_put(d->bdev, BDEV_RAW);
-		d->bdev = NULL;
-	}
-
+		blkdev_put(bdev, BDEV_RAW);
+	else
+		d->bdev = bdev;
 	return r;
 }
 

drivers/md/md.c

@@ -1046,12 +1046,9 @@ static int lock_rdev(mdk_rdev_t *rdev, dev_t dev)
 	int err = 0;
 	struct block_device *bdev;
 
-	bdev = bdget(dev);
-	if (!bdev)
-		return -ENOMEM;
-	err = blkdev_get(bdev, FMODE_READ|FMODE_WRITE, 0, BDEV_RAW);
-	if (err)
-		return err;
+	bdev = open_by_devnum(dev, FMODE_READ|FMODE_WRITE, BDEV_RAW);
+	if (IS_ERR(bdev))
+		return PTR_ERR(bdev);
 	err = bd_claim(bdev, rdev);
 	if (err) {
 		blkdev_put(bdev, BDEV_RAW);

drivers/mtd/devices/blkmtd.c

@@ -1128,9 +1128,8 @@ static int __init init_blkmtd(void)
     return 1;
   }
   /* get the block device */
-  bdev = bdget(rdev);
-  err = blkdev_get(bdev, mode, 0, BDEV_RAW);
-  if (err)
+  bdev = open_by_devnum(rdev, FMODE_READ, BDEV_RAW);
+  if (IS_ERR(bdev))
     return 1;
 
   DEBUG(1, "blkmtd: devname = %s\n", bdevname(bdev, b));

fs/block_dev.c

@@ -436,6 +436,23 @@ void bd_release(struct block_device *bdev)
 	spin_unlock(&bdev_lock);
 }
 
+/*
+ * Tries to open block device by device number.  Use it ONLY if you
+ * really do not have anything better - i.e. when you are behind a
+ * truly sucky interface and all you are given is a device number.  _Never_
+ * to be used for internal purposes.  If you ever need it - reconsider
+ * your API.
+ */
+struct block_device *open_by_devnum(dev_t dev, unsigned mode, int kind)
+{
+	struct block_device *bdev = bdget(dev);
+	int err = -ENOMEM;
+	int flags = mode & FMODE_WRITE ? O_RDWR : O_RDONLY;
+	if (bdev)
+		err = blkdev_get(bdev, mode, flags, kind);
+	return err ? ERR_PTR(err) : bdev;
+}
+
 /*
  * This routine checks whether a removable media has been changed,
  * and invalidates all buffer-cache-entries in that case. This

fs/ext3/super.c

@@ -384,20 +384,16 @@ void ext3_update_dynamic_rev(struct super_block *sb)
 static struct block_device *ext3_blkdev_get(dev_t dev)
 {
 	struct block_device *bdev;
-	int err = -ENODEV;
 	char b[BDEVNAME_SIZE];
 
-	bdev = bdget(dev);
-	if (bdev == NULL)
-		goto fail;
-	err = blkdev_get(bdev, FMODE_READ|FMODE_WRITE, 0, BDEV_FS);
-	if (err < 0)
+	bdev = open_by_devnum(dev, FMODE_READ|FMODE_WRITE, BDEV_FS);
+	if (IS_ERR(bdev))
 		goto fail;
 	return bdev;
 
 fail:
-	printk(KERN_ERR "EXT3: failed to open journal device %s: %d\n",
-			__bdevname(dev, b), err);
+	printk(KERN_ERR "EXT3: failed to open journal device %s: %ld\n",
+			__bdevname(dev, b), PTR_ERR(bdev));
 	return NULL;
 }
 

fs/jfs/jfs_logmgr.c

@@ -1105,13 +1105,10 @@ int lmLogOpen(struct super_block *sb, struct jfs_log ** logptr)
 	 */
       externalLog:
 
-	if (!(bdev = bdget(JFS_SBI(sb)->logdev))) {
-		rc = ENODEV;
-		goto free;
-	}
-
-	if ((rc = blkdev_get(bdev, FMODE_READ|FMODE_WRITE, 0, BDEV_FS))) {
-		rc = -rc;
+	bdev = open_by_devnum(JFS_SBI(sb)->logdev,
+					FMODE_READ|FMODE_WRITE, BDEV_FS);
+	if (IS_ERR(bdev)) {
+		rc = -PTR_ERR(bdev);
 		goto free;
 	}
 

fs/reiserfs/journal.c

@@ -1911,21 +1911,16 @@ static int journal_init_dev( struct super_block *super,
 
 	/* there is no "jdev" option and journal is on separate device */
 	if( ( !jdev_name || !jdev_name[ 0 ] ) ) {
-		journal -> j_dev_bd = bdget(jdev);
-		if( journal -> j_dev_bd )
-			result = blkdev_get( journal -> j_dev_bd, 
-					     blkdev_mode, 0, 
-					     BDEV_FS );
-		else
-			result = -ENOMEM;
-		if( result != 0 )
+		journal->j_dev_bd = open_by_devnum(jdev, blkdev_mode, BDEV_FS);
+		if (IS_ERR(journal->j_dev_bd)) {
+			result = PTR_ERR(journal->j_dev_bd);
+			journal->j_dev_bd = NULL;
 			printk( "sh-458: journal_init_dev: cannot init journal device\n '%s': %i", 
-				bdevname(journal->j_dev_bd, b), result );
-
-		else if (jdev != super->s_dev) {
+				__bdevname(jdev, b), result );
+			return result;
+		} else if (jdev != super->s_dev)
 			set_blocksize(journal->j_dev_bd, super->s_blocksize);
-		}
-		return result;
+		return 0;
 	}
 
 	journal -> j_dev_file = filp_open( jdev_name, 0, 0 );

include/linux/fs.h

@@ -1041,6 +1041,7 @@ extern void bd_forget(struct inode *inode);
 extern void bdput(struct block_device *);
 extern int blkdev_open(struct inode *, struct file *);
 extern int blkdev_close(struct inode *, struct file *);
+extern struct block_device *open_by_devnum(dev_t, unsigned, int);
 extern struct file_operations def_blk_fops;
 extern struct address_space_operations def_blk_aops;
 extern struct file_operations def_chr_fops;

kernel/ksyms.c

@@ -209,6 +209,7 @@ EXPORT_SYMBOL(bd_claim);
 EXPORT_SYMBOL(bd_release);
 EXPORT_SYMBOL(open_bdev_excl);
 EXPORT_SYMBOL(close_bdev_excl);
+EXPORT_SYMBOL(open_by_devnum);
 EXPORT_SYMBOL(__brelse);
 EXPORT_SYMBOL(__bforget);
 EXPORT_SYMBOL(ll_rw_block);

kernel/suspend.c

@@ -1161,15 +1161,14 @@ static int read_suspend_image(const char * specialfile, int noresume)
 		struct block_device *bdev;
 		printk("Resuming from device %s\n",
 				__bdevname(resume_device, b));
-		bdev = bdget(resume_device);
-		if (!bdev) {
-			printk("No such block device ?!\n");
-			BUG();
+		bdev = open_by_devnum(resume_device, FMODE_READ, BDEV_RAW);
+		if (IS_ERR(bdev)) {
+			error = PTR_ERR(bdev);
+		} else {
+			set_blocksize(bdev, PAGE_SIZE);
+			error = __read_suspend_image(bdev, cur, noresume);
+			blkdev_put(bdev, BDEV_RAW);
 		}
-		blkdev_get(bdev, FMODE_READ, O_RDONLY, BDEV_RAW);
-		set_blocksize(bdev, PAGE_SIZE);
-		error = __read_suspend_image(bdev, cur, noresume);
-		blkdev_put(bdev, BDEV_RAW);
 	} else error = -ENOMEM;
 
 	if (scratch_page)