[PATCH v6] Add cli and ioctl to forget scanned device(s)

[PATCH v6] Add cli and ioctl to forget scanned device(s)

[Anand Jain]

v6:
 Use the changed fn name btrfs_free_stale_devices().
 
 Change in title:
 Old v5:
 Cover-letter:
  [PATCH v5] Add cli and ioctl to ignore a scanned device
 Kernel:
  [PATCH v5] btrfs: introduce feature to ignore a btrfs device
 Progs:
  [PATCH v5] btrfs-progs: add 'btrfs device ignore' cli

v5:
  Adds feature to delete all stale devices
  Reuses btrfs_free_stale_devices() fn and so depends on the
    patch-set [1] in the ML.
  Uses struct btrfs_ioctl_vol_args_v2 instead of
    struct btrfs_ioctl_vol_args as arg
  Does the device path matching instead of btrfs_device matching
    (we won't delete the mounted device as btrfs_free_stale_devices()
    checks for it)
v4:
  No change. But as the ML thread may be confusing, so resend.
v3:
  No change. Send to correct ML.
v2:
  Accepts review from Nikolay, details are in the specific patch.
  Patch 1/2 is renamed from
    [PATCH 1/2] btrfs: refactor btrfs_free_stale_device() to get device list delete
  to
    [PATCH 1/2] btrfs: add function to device list delete

Adds cli and ioctl to forget a scanned device or forget all stale
devices in the kernel.

Anand Jain (1):
  btrfs: introduce feature to forget a btrfs device

 fs/btrfs/super.c           | 27 +++++++++++++++++++++++----
 fs/btrfs/volumes.c         |  9 +++++++++
 fs/btrfs/volumes.h         |  1 +
 include/uapi/linux/btrfs.h |  6 +++++-
 4 files changed, 38 insertions(+), 5 deletions(-)

Anand Jain (1):
  btrfs-progs: add cli to forget one or all scanned devices

 cmds-device.c | 77 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 ioctl.h       |  6 ++++-
 2 files changed, 82 insertions(+), 1 deletion(-)

-- 
2.7.0

[PATCH 1/1] btrfs: introduce feature to forget a btrfs device

[Anand Jain]

Support for a new command 'btrfs dev forget [dev]' is proposed here,
to undo the effects of 'btrfs dev scan [dev]'. For this purpose,
this patch proposes to use ioctl #5 as it was empty.
	IOW(BTRFS_IOCTL_MAGIC, 5, ..)
This patch adds new ioctl BTRFS_IOC_FORGET_DEV which can be sent from
the /dev/btrfs-control to forget one or all devices, (devices which are
not mounted) from the btrfs kernel.

The argument it takes is struct btrfs_ioctl_vol_args_v2, and ::name can be
set to specify the device path. And all unmounted devices can be removed
from the kernel using the BTRFS_DEVICE_SPEC_ALL_DEV flag. Remove all
devices functionality would override remove one device when both are
specified in an IOCTL call.
Again, the devices are removed only if the relevant fsid aren't mounted.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
---
 fs/btrfs/super.c           | 27 +++++++++++++++++++++++----
 fs/btrfs/volumes.c         |  9 +++++++++
 fs/btrfs/volumes.h         |  1 +
 include/uapi/linux/btrfs.h |  6 +++++-
 4 files changed, 38 insertions(+), 5 deletions(-)

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 559fc53ff59e..6a9a5ce8af3b 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -2219,21 +2219,37 @@ static long btrfs_control_ioctl(struct file *file, unsigned int cmd,
 				unsigned long arg)
 {
 	struct btrfs_ioctl_vol_args *vol;
+	struct btrfs_ioctl_vol_args_v2 *vol2;
 	struct btrfs_fs_devices *fs_devices;
 	int ret = -ENOTTY;
 
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
 
-	vol = memdup_user((void __user *)arg, sizeof(*vol));
-	if (IS_ERR(vol))
-		return PTR_ERR(vol);
+	if (cmd == BTRFS_IOC_FORGET_DEV) {
+		vol2 = memdup_user((void __user *)arg, sizeof(*vol2));
+		if (IS_ERR(vol2))
+			return PTR_ERR(vol2);
+
+		if (vol2->flags & ~BTRFS_VOL_ARG_V2_FLAGS_SUPPORTED)
+			return -EOPNOTSUPP;
+	} else {
+		vol = memdup_user((void __user *)arg, sizeof(*vol));
+		if (IS_ERR(vol))
+			return PTR_ERR(vol);
+	}
 
 	switch (cmd) {
 	case BTRFS_IOC_SCAN_DEV:
 		ret = btrfs_scan_one_device(vol->name, FMODE_READ,
 					    &btrfs_fs_type, &fs_devices);
 		break;
+	case BTRFS_IOC_FORGET_DEV:
+		if (vol2->flags & BTRFS_DEVICE_SPEC_ALL_DEV)
+			ret = btrfs_forget_devices(NULL);
+		else
+			ret = btrfs_forget_devices(vol2->name);
+		break;
 	case BTRFS_IOC_DEVICES_READY:
 		ret = btrfs_scan_one_device(vol->name, FMODE_READ,
 					    &btrfs_fs_type, &fs_devices);
@@ -2246,7 +2262,10 @@ static long btrfs_control_ioctl(struct file *file, unsigned int cmd,
 		break;
 	}
 
-	kfree(vol);
+	if (cmd == BTRFS_IOC_FORGET_DEV)
+		kfree(vol2);
+	else
+		kfree(vol);
 	return ret;
 }
 
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index e947e47f8fff..b0c9948baf9a 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -1171,6 +1171,15 @@ static int btrfs_read_disk_super(struct block_device *bdev, u64 bytenr,
 	return 0;
 }
 
+int btrfs_forget_devices(const char *path)
+{
+	mutex_lock(&uuid_mutex);
+	btrfs_free_stale_devices(path, NULL);
+	mutex_unlock(&uuid_mutex);
+
+	return 0;
+}
+
 /*
  * Look for a btrfs signature on a device. This may be called out of the mount path
  * and we are not allowed to call set_blocksize during the scan. The superblock
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 15216fed918b..b954ca3b79a9 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -422,6 +422,7 @@ int btrfs_open_devices(struct btrfs_fs_devices *fs_devices,
 		       fmode_t flags, void *holder);
 int btrfs_scan_one_device(const char *path, fmode_t flags, void *holder,
 			  struct btrfs_fs_devices **fs_devices_ret);
+int btrfs_forget_devices(const char *path);
 int btrfs_close_devices(struct btrfs_fs_devices *fs_devices);
 void btrfs_close_extra_devices(struct btrfs_fs_devices *fs_devices, int step);
 void btrfs_assign_next_active_device(struct btrfs_fs_info *fs_info,
diff --git a/include/uapi/linux/btrfs.h b/include/uapi/linux/btrfs.h
index c8d99b9ca550..4e8ec1391872 100644
--- a/include/uapi/linux/btrfs.h
+++ b/include/uapi/linux/btrfs.h
@@ -41,12 +41,14 @@ struct btrfs_ioctl_vol_args {
 #define BTRFS_SUBVOL_QGROUP_INHERIT	(1ULL << 2)
 
 #define BTRFS_DEVICE_SPEC_BY_ID		(1ULL << 3)
+#define BTRFS_DEVICE_SPEC_ALL_DEV	(1ULL << 4)
 
 #define BTRFS_VOL_ARG_V2_FLAGS_SUPPORTED		\
 			(BTRFS_SUBVOL_CREATE_ASYNC |	\
 			BTRFS_SUBVOL_RDONLY |		\
 			BTRFS_SUBVOL_QGROUP_INHERIT |	\
-			BTRFS_DEVICE_SPEC_BY_ID)
+			BTRFS_DEVICE_SPEC_BY_ID |	\
+			BTRFS_DEVICE_SPEC_ALL_DEV)
 
 #define BTRFS_FSID_SIZE 16
 #define BTRFS_UUID_SIZE 16
@@ -745,6 +747,8 @@ enum btrfs_err_code {
 				   struct btrfs_ioctl_vol_args)
 #define BTRFS_IOC_SCAN_DEV _IOW(BTRFS_IOCTL_MAGIC, 4, \
 				   struct btrfs_ioctl_vol_args)
+#define BTRFS_IOC_FORGET_DEV _IOW(BTRFS_IOCTL_MAGIC, 5, \
+				   struct btrfs_ioctl_vol_args)
 /* trans start and trans end are dangerous, and only for
  * use by applications that know how to avoid the
  * resulting deadlocks
-- 
2.7.0

[PATCH 1/1] btrfs-progs: add cli to forget one or all scanned devices

[Anand Jain]

This patch adds cli
  btrfs device forget [dev]
which shall remove the relevant device entries in the kernel
matching the dev. If no argument is given it shall remove all
stale (device which are not mounted) from the kernel.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
---
 cmds-device.c | 77 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 ioctl.h       |  6 ++++-
 2 files changed, 82 insertions(+), 1 deletion(-)

diff --git a/cmds-device.c b/cmds-device.c
index f4cdb39f64ac..8c3ad3080437 100644
--- a/cmds-device.c
+++ b/cmds-device.c
@@ -329,6 +329,82 @@ out:
 	return !!ret;
 }
 
+static const char * const cmd_device_forget_usage[] = {
+	"btrfs device forget [<device>]",
+	"Forget a scanned device or all stale devices in the btrfs.ko",
+	NULL
+};
+
+static int btrfs_forget_devices(void)
+{
+	struct btrfs_ioctl_vol_args_v2 args;
+	int fd;
+	int ret;
+
+	fd = open("/dev/btrfs-control", O_RDWR);
+	if (fd < 0)
+		return -errno;
+
+	memset(&args, 0, sizeof(args));
+	args.flags = BTRFS_DEVICE_SPEC_ALL;
+	ret = ioctl(fd, BTRFS_IOC_FORGET_DEV, &args);
+	if (ret)
+		ret = -errno;
+	close(fd);
+	return ret;
+
+}
+
+static int btrfs_forget_one_device(char *path)
+{
+	struct btrfs_ioctl_vol_args_v2 args;
+	int fd;
+	int ret;
+
+	fd = open("/dev/btrfs-control", O_RDWR);
+	if (fd < 0)
+		return -errno;
+
+	memset(&args, 0, sizeof(args));
+	strncpy_null(args.name, path);
+	ret = ioctl(fd, BTRFS_IOC_FORGET_DEV, &args);
+	if (ret)
+		ret = -errno;
+	close(fd);
+	return ret;
+}
+
+static int cmd_device_forget(int argc, char **argv)
+{
+	char *path;
+	int ret = 0;
+
+	if (check_argc_max(argc - optind, 1))
+		usage(cmd_device_forget_usage);
+
+	if (argc == 1) {
+		ret = btrfs_forget_devices();
+		if (ret)
+			error("Can't forget: %s", strerror(-ret));
+		return ret;
+	}
+
+	path = canonicalize_path(argv[1]);
+	if (!path) {
+		error("Could not canonicalize path '%s': %s",
+					argv[1], strerror(errno));
+		return -ENOENT;
+	}
+
+	ret  = btrfs_forget_one_device(path);
+	if (ret)
+		error("Can't forget '%s': %s", path, strerror(-ret));
+
+	free(path);
+
+	return ret;
+}
+
 static const char * const cmd_device_ready_usage[] = {
 	"btrfs device ready <device>",
 	"Check device to see if it has all of its devices in cache for mounting",
@@ -604,6 +680,7 @@ const struct cmd_group device_cmd_group = {
 			CMD_ALIAS },
 		{ "remove", cmd_device_remove, cmd_device_remove_usage, NULL, 0 },
 		{ "scan", cmd_device_scan, cmd_device_scan_usage, NULL, 0 },
+		{ "forget", cmd_device_forget, cmd_device_forget_usage, NULL, 0 },
 		{ "ready", cmd_device_ready, cmd_device_ready_usage, NULL, 0 },
 		{ "stats", cmd_device_stats, cmd_device_stats_usage, NULL, 0 },
 		{ "usage", cmd_device_usage,
diff --git a/ioctl.h b/ioctl.h
index 709e996f401c..ac697f044950 100644
--- a/ioctl.h
+++ b/ioctl.h
@@ -53,12 +53,14 @@ BUILD_ASSERT(sizeof(struct btrfs_ioctl_vol_args) == 4096);
 #define BTRFS_SUBVOL_RDONLY		(1ULL << 1)
 #define BTRFS_SUBVOL_QGROUP_INHERIT	(1ULL << 2)
 #define BTRFS_DEVICE_SPEC_BY_ID		(1ULL << 3)
+#define BTRFS_DEVICE_SPEC_ALL		(1ULL << 4)
 
 #define BTRFS_VOL_ARG_V2_FLAGS_SUPPORTED		\
 			(BTRFS_SUBVOL_CREATE_ASYNC |	\
 			BTRFS_SUBVOL_RDONLY |		\
 			BTRFS_SUBVOL_QGROUP_INHERIT |	\
-			BTRFS_DEVICE_SPEC_BY_ID)
+			BTRFS_DEVICE_SPEC_BY_ID |	\
+			BTRFS_DEVICE_SPEC_ALL)
 
 #define BTRFS_FSID_SIZE 16
 #define BTRFS_UUID_SIZE 16
@@ -721,6 +723,8 @@ static inline char *btrfs_err_str(enum btrfs_err_code err_code)
 				   struct btrfs_ioctl_vol_args)
 #define BTRFS_IOC_SCAN_DEV _IOW(BTRFS_IOCTL_MAGIC, 4, \
 				   struct btrfs_ioctl_vol_args)
+#define BTRFS_IOC_FORGET_DEV _IOW(BTRFS_IOCTL_MAGIC, 5, \
+				   struct btrfs_ioctl_vol_args)
 /* trans start and trans end are dangerous, and only for
  * use by applications that know how to avoid the
  * resulting deadlocks
-- 
2.7.0

Re: [PATCH 1/1] btrfs: introduce feature to forget a btrfs device

[Liu Bo]

On Thu, Jan 11, 2018 at 09:25:50AM +0800, Anand Jain wrote:
> Support for a new command 'btrfs dev forget [dev]' is proposed here,
> to undo the effects of 'btrfs dev scan [dev]'. For this purpose,
> this patch proposes to use ioctl #5 as it was empty.
> 	IOW(BTRFS_IOCTL_MAGIC, 5, ..)
> This patch adds new ioctl BTRFS_IOC_FORGET_DEV which can be sent from
> the /dev/btrfs-control to forget one or all devices, (devices which are
> not mounted) from the btrfs kernel.
>

To me this seems to offer a debugging ability, could you please
elaborate the use case where we need to forget a particular device
instead of just wiping the uuid?

Thanks,

-liubo
> The argument it takes is struct btrfs_ioctl_vol_args_v2, and ::name can be
> set to specify the device path. And all unmounted devices can be removed
> from the kernel using the BTRFS_DEVICE_SPEC_ALL_DEV flag. Remove all
> devices functionality would override remove one device when both are
> specified in an IOCTL call.
> Again, the devices are removed only if the relevant fsid aren't mounted.
> 
> Signed-off-by: Anand Jain <anand.jain@oracle.com>
> ---
>  fs/btrfs/super.c           | 27 +++++++++++++++++++++++----
>  fs/btrfs/volumes.c         |  9 +++++++++
>  fs/btrfs/volumes.h         |  1 +
>  include/uapi/linux/btrfs.h |  6 +++++-
>  4 files changed, 38 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
> index 559fc53ff59e..6a9a5ce8af3b 100644
> --- a/fs/btrfs/super.c
> +++ b/fs/btrfs/super.c
> @@ -2219,21 +2219,37 @@ static long btrfs_control_ioctl(struct file *file, unsigned int cmd,
>  				unsigned long arg)
>  {
>  	struct btrfs_ioctl_vol_args *vol;
> +	struct btrfs_ioctl_vol_args_v2 *vol2;
>  	struct btrfs_fs_devices *fs_devices;
>  	int ret = -ENOTTY;
>  
>  	if (!capable(CAP_SYS_ADMIN))
>  		return -EPERM;
>  
> -	vol = memdup_user((void __user *)arg, sizeof(*vol));
> -	if (IS_ERR(vol))
> -		return PTR_ERR(vol);
> +	if (cmd == BTRFS_IOC_FORGET_DEV) {
> +		vol2 = memdup_user((void __user *)arg, sizeof(*vol2));
> +		if (IS_ERR(vol2))
> +			return PTR_ERR(vol2);
> +
> +		if (vol2->flags & ~BTRFS_VOL_ARG_V2_FLAGS_SUPPORTED)
> +			return -EOPNOTSUPP;
> +	} else {
> +		vol = memdup_user((void __user *)arg, sizeof(*vol));
> +		if (IS_ERR(vol))
> +			return PTR_ERR(vol);
> +	}
>  
>  	switch (cmd) {
>  	case BTRFS_IOC_SCAN_DEV:
>  		ret = btrfs_scan_one_device(vol->name, FMODE_READ,
>  					    &btrfs_fs_type, &fs_devices);
>  		break;
> +	case BTRFS_IOC_FORGET_DEV:
> +		if (vol2->flags & BTRFS_DEVICE_SPEC_ALL_DEV)
> +			ret = btrfs_forget_devices(NULL);
> +		else
> +			ret = btrfs_forget_devices(vol2->name);
> +		break;
>  	case BTRFS_IOC_DEVICES_READY:
>  		ret = btrfs_scan_one_device(vol->name, FMODE_READ,
>  					    &btrfs_fs_type, &fs_devices);
> @@ -2246,7 +2262,10 @@ static long btrfs_control_ioctl(struct file *file, unsigned int cmd,
>  		break;
>  	}
>  
> -	kfree(vol);
> +	if (cmd == BTRFS_IOC_FORGET_DEV)
> +		kfree(vol2);
> +	else
> +		kfree(vol);
>  	return ret;
>  }
>  
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index e947e47f8fff..b0c9948baf9a 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -1171,6 +1171,15 @@ static int btrfs_read_disk_super(struct block_device *bdev, u64 bytenr,
>  	return 0;
>  }
>  
> +int btrfs_forget_devices(const char *path)
> +{
> +	mutex_lock(&uuid_mutex);
> +	btrfs_free_stale_devices(path, NULL);
> +	mutex_unlock(&uuid_mutex);
> +
> +	return 0;
> +}
> +
>  /*
>   * Look for a btrfs signature on a device. This may be called out of the mount path
>   * and we are not allowed to call set_blocksize during the scan. The superblock
> diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
> index 15216fed918b..b954ca3b79a9 100644
> --- a/fs/btrfs/volumes.h
> +++ b/fs/btrfs/volumes.h
> @@ -422,6 +422,7 @@ int btrfs_open_devices(struct btrfs_fs_devices *fs_devices,
>  		       fmode_t flags, void *holder);
>  int btrfs_scan_one_device(const char *path, fmode_t flags, void *holder,
>  			  struct btrfs_fs_devices **fs_devices_ret);
> +int btrfs_forget_devices(const char *path);
>  int btrfs_close_devices(struct btrfs_fs_devices *fs_devices);
>  void btrfs_close_extra_devices(struct btrfs_fs_devices *fs_devices, int step);
>  void btrfs_assign_next_active_device(struct btrfs_fs_info *fs_info,
> diff --git a/include/uapi/linux/btrfs.h b/include/uapi/linux/btrfs.h
> index c8d99b9ca550..4e8ec1391872 100644
> --- a/include/uapi/linux/btrfs.h
> +++ b/include/uapi/linux/btrfs.h
> @@ -41,12 +41,14 @@ struct btrfs_ioctl_vol_args {
>  #define BTRFS_SUBVOL_QGROUP_INHERIT	(1ULL << 2)
>  
>  #define BTRFS_DEVICE_SPEC_BY_ID		(1ULL << 3)
> +#define BTRFS_DEVICE_SPEC_ALL_DEV	(1ULL << 4)
>  
>  #define BTRFS_VOL_ARG_V2_FLAGS_SUPPORTED		\
>  			(BTRFS_SUBVOL_CREATE_ASYNC |	\
>  			BTRFS_SUBVOL_RDONLY |		\
>  			BTRFS_SUBVOL_QGROUP_INHERIT |	\
> -			BTRFS_DEVICE_SPEC_BY_ID)
> +			BTRFS_DEVICE_SPEC_BY_ID |	\
> +			BTRFS_DEVICE_SPEC_ALL_DEV)
>  
>  #define BTRFS_FSID_SIZE 16
>  #define BTRFS_UUID_SIZE 16
> @@ -745,6 +747,8 @@ enum btrfs_err_code {
>  				   struct btrfs_ioctl_vol_args)
>  #define BTRFS_IOC_SCAN_DEV _IOW(BTRFS_IOCTL_MAGIC, 4, \
>  				   struct btrfs_ioctl_vol_args)
> +#define BTRFS_IOC_FORGET_DEV _IOW(BTRFS_IOCTL_MAGIC, 5, \
> +				   struct btrfs_ioctl_vol_args)
>  /* trans start and trans end are dangerous, and only for
>   * use by applications that know how to avoid the
>   * resulting deadlocks
> -- 
> 2.7.0
> 
> --
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> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: [PATCH 1/1] btrfs: introduce feature to forget a btrfs device

[Anand Jain]

On 02/28/2018 08:57 AM, Liu Bo wrote:
> On Thu, Jan 11, 2018 at 09:25:50AM +0800, Anand Jain wrote:
>> Support for a new command 'btrfs dev forget [dev]' is proposed here,
>> to undo the effects of 'btrfs dev scan [dev]'. For this purpose,
>> this patch proposes to use ioctl #5 as it was empty.
>> 	IOW(BTRFS_IOCTL_MAGIC, 5, ..)
>> This patch adds new ioctl BTRFS_IOC_FORGET_DEV which can be sent from
>> the /dev/btrfs-control to forget one or all devices, (devices which are
>> not mounted) from the btrfs kernel.
>>
> 
> To me this seems to offer a debugging ability, could you please
> elaborate the use case where we need to forget a particular device
> instead of just wiping the uuid?


Right, debug is one use case, the other use case is to recover from
the split brain scenario [1].
When it happens we need to bring user's attention to decide which
disk is good and needs a way to un-scan/forget the device so that
the FS can be mounted with a disk missing.

[1]
  https://patchwork.kernel.org/patch/10055145/

Thanks, Anand


> Thanks,
> 
> -liubo
>> The argument it takes is struct btrfs_ioctl_vol_args_v2, and ::name can be
>> set to specify the device path. And all unmounted devices can be removed
>> from the kernel using the BTRFS_DEVICE_SPEC_ALL_DEV flag. Remove all
>> devices functionality would override remove one device when both are
>> specified in an IOCTL call.
>> Again, the devices are removed only if the relevant fsid aren't mounted.
>>
>> Signed-off-by: Anand Jain <anand.jain@oracle.com>
>> ---
>>   fs/btrfs/super.c           | 27 +++++++++++++++++++++++----
>>   fs/btrfs/volumes.c         |  9 +++++++++
>>   fs/btrfs/volumes.h         |  1 +
>>   include/uapi/linux/btrfs.h |  6 +++++-
>>   4 files changed, 38 insertions(+), 5 deletions(-)
>>
>> diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
>> index 559fc53ff59e..6a9a5ce8af3b 100644
>> --- a/fs/btrfs/super.c
>> +++ b/fs/btrfs/super.c
>> @@ -2219,21 +2219,37 @@ static long btrfs_control_ioctl(struct file *file, unsigned int cmd,
>>   				unsigned long arg)
>>   {
>>   	struct btrfs_ioctl_vol_args *vol;
>> +	struct btrfs_ioctl_vol_args_v2 *vol2;
>>   	struct btrfs_fs_devices *fs_devices;
>>   	int ret = -ENOTTY;
>>   
>>   	if (!capable(CAP_SYS_ADMIN))
>>   		return -EPERM;
>>   
>> -	vol = memdup_user((void __user *)arg, sizeof(*vol));
>> -	if (IS_ERR(vol))
>> -		return PTR_ERR(vol);
>> +	if (cmd == BTRFS_IOC_FORGET_DEV) {
>> +		vol2 = memdup_user((void __user *)arg, sizeof(*vol2));
>> +		if (IS_ERR(vol2))
>> +			return PTR_ERR(vol2);
>> +
>> +		if (vol2->flags & ~BTRFS_VOL_ARG_V2_FLAGS_SUPPORTED)
>> +			return -EOPNOTSUPP;
>> +	} else {
>> +		vol = memdup_user((void __user *)arg, sizeof(*vol));
>> +		if (IS_ERR(vol))
>> +			return PTR_ERR(vol);
>> +	}
>>   
>>   	switch (cmd) {
>>   	case BTRFS_IOC_SCAN_DEV:
>>   		ret = btrfs_scan_one_device(vol->name, FMODE_READ,
>>   					    &btrfs_fs_type, &fs_devices);
>>   		break;
>> +	case BTRFS_IOC_FORGET_DEV:
>> +		if (vol2->flags & BTRFS_DEVICE_SPEC_ALL_DEV)
>> +			ret = btrfs_forget_devices(NULL);
>> +		else
>> +			ret = btrfs_forget_devices(vol2->name);
>> +		break;
>>   	case BTRFS_IOC_DEVICES_READY:
>>   		ret = btrfs_scan_one_device(vol->name, FMODE_READ,
>>   					    &btrfs_fs_type, &fs_devices);
>> @@ -2246,7 +2262,10 @@ static long btrfs_control_ioctl(struct file *file, unsigned int cmd,
>>   		break;
>>   	}
>>   
>> -	kfree(vol);
>> +	if (cmd == BTRFS_IOC_FORGET_DEV)
>> +		kfree(vol2);
>> +	else
>> +		kfree(vol);
>>   	return ret;
>>   }
>>   
>> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
>> index e947e47f8fff..b0c9948baf9a 100644
>> --- a/fs/btrfs/volumes.c
>> +++ b/fs/btrfs/volumes.c
>> @@ -1171,6 +1171,15 @@ static int btrfs_read_disk_super(struct block_device *bdev, u64 bytenr,
>>   	return 0;
>>   }
>>   
>> +int btrfs_forget_devices(const char *path)
>> +{
>> +	mutex_lock(&uuid_mutex);
>> +	btrfs_free_stale_devices(path, NULL);
>> +	mutex_unlock(&uuid_mutex);
>> +
>> +	return 0;
>> +}
>> +
>>   /*
>>    * Look for a btrfs signature on a device. This may be called out of the mount path
>>    * and we are not allowed to call set_blocksize during the scan. The superblock
>> diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
>> index 15216fed918b..b954ca3b79a9 100644
>> --- a/fs/btrfs/volumes.h
>> +++ b/fs/btrfs/volumes.h
>> @@ -422,6 +422,7 @@ int btrfs_open_devices(struct btrfs_fs_devices *fs_devices,
>>   		       fmode_t flags, void *holder);
>>   int btrfs_scan_one_device(const char *path, fmode_t flags, void *holder,
>>   			  struct btrfs_fs_devices **fs_devices_ret);
>> +int btrfs_forget_devices(const char *path);
>>   int btrfs_close_devices(struct btrfs_fs_devices *fs_devices);
>>   void btrfs_close_extra_devices(struct btrfs_fs_devices *fs_devices, int step);
>>   void btrfs_assign_next_active_device(struct btrfs_fs_info *fs_info,
>> diff --git a/include/uapi/linux/btrfs.h b/include/uapi/linux/btrfs.h
>> index c8d99b9ca550..4e8ec1391872 100644
>> --- a/include/uapi/linux/btrfs.h
>> +++ b/include/uapi/linux/btrfs.h
>> @@ -41,12 +41,14 @@ struct btrfs_ioctl_vol_args {
>>   #define BTRFS_SUBVOL_QGROUP_INHERIT	(1ULL << 2)
>>   
>>   #define BTRFS_DEVICE_SPEC_BY_ID		(1ULL << 3)
>> +#define BTRFS_DEVICE_SPEC_ALL_DEV	(1ULL << 4)
>>   
>>   #define BTRFS_VOL_ARG_V2_FLAGS_SUPPORTED		\
>>   			(BTRFS_SUBVOL_CREATE_ASYNC |	\
>>   			BTRFS_SUBVOL_RDONLY |		\
>>   			BTRFS_SUBVOL_QGROUP_INHERIT |	\
>> -			BTRFS_DEVICE_SPEC_BY_ID)
>> +			BTRFS_DEVICE_SPEC_BY_ID |	\
>> +			BTRFS_DEVICE_SPEC_ALL_DEV)
>>   
>>   #define BTRFS_FSID_SIZE 16
>>   #define BTRFS_UUID_SIZE 16
>> @@ -745,6 +747,8 @@ enum btrfs_err_code {
>>   				   struct btrfs_ioctl_vol_args)
>>   #define BTRFS_IOC_SCAN_DEV _IOW(BTRFS_IOCTL_MAGIC, 4, \
>>   				   struct btrfs_ioctl_vol_args)
>> +#define BTRFS_IOC_FORGET_DEV _IOW(BTRFS_IOCTL_MAGIC, 5, \
>> +				   struct btrfs_ioctl_vol_args)
>>   /* trans start and trans end are dangerous, and only for
>>    * use by applications that know how to avoid the
>>    * resulting deadlocks
>> -- 
>> 2.7.0
>>
>> --
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