[2/2] btrfs: check generation as replace duplicates devid+uuid

Commit Message

Anand Jain June 13, 2014, 4:26 a.m. UTC

From: Anand Jain <[e-mail]>

When FS in unmounted we need to check generation number as well
since devid+uuid combination could match with the missing replaced
disk when it reappears, and without this patch it might pair with
the replaced disk again.

 device_list_add() function is called in the following threads,
	mount device option
	mount argument
	ioctl BTRFS_IOC_SCAN_DEV (btrfs dev scan)
	ioctl BTRFS_IOC_DEVICES_READY (btrfs dev ready <dev>)
 they have been unit tested to work fine with this patch.

 If the user knows what he is doing and really want to pair with
 replaced disk (which is not a standard operation), then he should
 first clear the kernel btrfs device list in the memory by doing
 the module unload/load and followed with the mount -o device option.

Signed-off-by: Anand Jain <[e-mail]>
---
 fs/btrfs/volumes.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

Comments

Wang Shilong July 1, 2014, 7:39 a.m. UTC | #1

Hi Anand,

On 06/13/2014 12:26 PM, Anand Jain wrote:
>   
<..snip..>
> @@ -523,6 +523,16 @@ static noinline int device_list_add(const char *path,
>   
>   		if (fs_devices->opened)
>   			return -EBUSY;
> +		else {
> +			/*
> +			 * That is if the FS is _not_ mounted and if you are here, that
> +			 * means there is more than one disk with same uuid and devid.
> +			 * We keep the one with larger generation number or the last-in
> +			 * if generation are equal.
> +			 */
> +			if (found_transid < device->generation)
> +				return -EINVAL;
> +		}
I tried this patch it outputed the following message if it encounter two 
device with the same uuid and device id:

Scanning for Btrfs filesystems
ERROR: device scan failed '/dev/sdc' - Invalid argument

Same comment as your first patch here.
>   
>   		name = rcu_string_strdup(path, GFP_NOFS);
>   		if (!name)
> @@ -535,6 +545,15 @@ static noinline int device_list_add(const char *path,
>   		}
>   	}
>   
> +	/*
> +	 * Unmount does not free the btrfs_device struct but would zero
> +	 * generation along with most of the other members. So just update
> +	 * it back. We need it to pick the disk with largest generation
> +	 * (as above).
> +	 */
> +	if (!fs_devices->opened)
> +		device->generation = found_transid;
> +
>   	if (found_transid > fs_devices->latest_trans) {
>   		fs_devices->latest_devid = devid;
>   		fs_devices->latest_trans = found_transid;

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Patch

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 56822f0..bb1b4bd 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -523,6 +523,16 @@  static noinline int device_list_add(const char *path,
 
 		if (fs_devices->opened)
 			return -EBUSY;
+		else {
+			/*
+			 * That is if the FS is _not_ mounted and if you are here, that
+			 * means there is more than one disk with same uuid and devid.
+			 * We keep the one with larger generation number or the last-in
+			 * if generation are equal.
+			 */
+			if (found_transid < device->generation)
+				return -EINVAL;
+		}
 
 		name = rcu_string_strdup(path, GFP_NOFS);
 		if (!name)
@@ -535,6 +545,15 @@  static noinline int device_list_add(const char *path,
 		}
 	}
 
+	/*
+	 * Unmount does not free the btrfs_device struct but would zero
+	 * generation along with most of the other members. So just update
+	 * it back. We need it to pick the disk with largest generation
+	 * (as above).
+	 */
+	if (!fs_devices->opened)
+		device->generation = found_transid;
+
 	if (found_transid > fs_devices->latest_trans) {
 		fs_devices->latest_devid = devid;
 		fs_devices->latest_trans = found_transid;