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From: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Date: Wed, 14 Feb 2024 08:42:12 -0800
Subject: [PATCH 1/5] btrfs: always open the device read-only in
 btrfs_scan_one_device
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Message-Id: <20240214-hch-device-open-v1-1-b153428b4f72@wdc.com>
References: <20240214-hch-device-open-v1-0-b153428b4f72@wdc.com>
In-Reply-To: <20240214-hch-device-open-v1-0-b153428b4f72@wdc.com>
To: Chris Mason <clm@fb.com>, Josef Bacik <josef@toxicpanda.com>, 
 David Sterba <dsterba@suse.com>, Christoph Hellwig <hch@lst.de>
Cc: Johannes Thumshirn <johannes.thumshirn@wdc.com>, 
 linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org

From: Christoph Hellwig <hch@lst.de>

btrfs_scan_one_device opens the block device only to read the super
block.  Instead of passing a blk_mode_t argument to sometimes open
it for writing, just hard code BLK_OPEN_READ as it will never write
to the device or hand the block_device out to someone else.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
---
 fs/btrfs/super.c   | 9 ++++-----
 fs/btrfs/volumes.c | 4 ++--
 fs/btrfs/volumes.h | 2 +-
 3 files changed, 7 insertions(+), 8 deletions(-)

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 40ae264fd3ed..b6cadf4f21b8 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -299,10 +299,9 @@ static int btrfs_parse_param(struct fs_context *fc, struct fs_parameter *param)
 		break;
 	case Opt_device: {
 		struct btrfs_device *device;
-		blk_mode_t mode = btrfs_open_mode(fc);
 
 		mutex_lock(&uuid_mutex);
-		device = btrfs_scan_one_device(param->string, mode, false);
+		device = btrfs_scan_one_device(param->string, false);
 		mutex_unlock(&uuid_mutex);
 		if (IS_ERR(device))
 			return PTR_ERR(device);
@@ -1808,7 +1807,7 @@ static int btrfs_get_tree_super(struct fs_context *fc)
 	 * With 'true' passed to btrfs_scan_one_device() (mount time) we expect
 	 * either a valid device or an error.
 	 */
-	device = btrfs_scan_one_device(fc->source, mode, true);
+	device = btrfs_scan_one_device(fc->source, true);
 	ASSERT(device != NULL);
 	if (IS_ERR(device)) {
 		mutex_unlock(&uuid_mutex);
@@ -2210,7 +2209,7 @@ static long btrfs_control_ioctl(struct file *file, unsigned int cmd,
 		 * Scanning outside of mount can return NULL which would turn
 		 * into 0 error code.
 		 */
-		device = btrfs_scan_one_device(vol->name, BLK_OPEN_READ, false);
+		device = btrfs_scan_one_device(vol->name, false);
 		ret = PTR_ERR_OR_ZERO(device);
 		mutex_unlock(&uuid_mutex);
 		break;
@@ -2228,7 +2227,7 @@ static long btrfs_control_ioctl(struct file *file, unsigned int cmd,
 		 * Scanning outside of mount can return NULL which would turn
 		 * into 0 error code.
 		 */
-		device = btrfs_scan_one_device(vol->name, BLK_OPEN_READ, false);
+		device = btrfs_scan_one_device(vol->name, false);
 		if (IS_ERR_OR_NULL(device)) {
 			mutex_unlock(&uuid_mutex);
 			ret = PTR_ERR(device);
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 4ad9eca9b46c..44caf1a48d33 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -1308,7 +1308,7 @@ int btrfs_forget_devices(dev_t devt)
  * the device or return an error. Multi-device and seeding devices are registered
  * in both cases.
  */
-struct btrfs_device *btrfs_scan_one_device(const char *path, blk_mode_t flags,
+struct btrfs_device *btrfs_scan_one_device(const char *path,
 					   bool mount_arg_dev)
 {
 	struct btrfs_super_block *disk_super;
@@ -1337,7 +1337,7 @@ struct btrfs_device *btrfs_scan_one_device(const char *path, blk_mode_t flags,
 	 * values temporarily, as the device paths of the fsid are the only
 	 * required information for assembling the volume.
 	 */
-	bdev_handle = bdev_open_by_path(path, flags, NULL, NULL);
+	bdev_handle = bdev_open_by_path(path, BLK_OPEN_READ, NULL, NULL);
 	if (IS_ERR(bdev_handle))
 		return ERR_CAST(bdev_handle);
 
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 21d4de0e3f1f..97c7284e7565 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -655,7 +655,7 @@ struct btrfs_block_group *btrfs_create_chunk(struct btrfs_trans_handle *trans,
 void btrfs_mapping_tree_free(struct btrfs_fs_info *fs_info);
 int btrfs_open_devices(struct btrfs_fs_devices *fs_devices,
 		       blk_mode_t flags, void *holder);
-struct btrfs_device *btrfs_scan_one_device(const char *path, blk_mode_t flags,
+struct btrfs_device *btrfs_scan_one_device(const char *path,
 					   bool mount_arg_dev);
 int btrfs_forget_devices(dev_t devt);
 void btrfs_close_devices(struct btrfs_fs_devices *fs_devices);

-- 
2.43.0