[PATCH RESEND v12] Add cli and ioctl to forget scanned device(s)

[PATCH RESEND v12] Add cli and ioctl to forget scanned device(s)

[Anand Jain]

v12:
  Fixed coding style - leave space between " : ".

v11:
 btrfs-progs: Bring the code into the else part of if(forget).
	      Use strerror to print the erorr instead of ret.

v10:
 Make btrfs-progs changes more readable.
 With an effort to keep the known bug [1] as it is..
  [1]
   The cli 'btrfs device scan --all /dev/sdb' which should have scanned
    only one device, ends up scanning all the devices and I am not trying
    to fix this bug in this patch because..
  . -d|--all is marked as deprecated, I hope -d option would go away
  . For now some script might be using this bug as a feature, and fixing
    this bug might lead to mount failure.

v9:
 Make forget as a btrfs device scan option.
 Use forget in the fstests, now you can run fstests with btrfs as rootfs
  which helps to exercise the uuid_mutex lock.

v8:
 Change log update in the kernel patch.

v7:
 Use struct btrfs_ioctl_vol_args (instead of struct
  btrfs_ioctl_vol_args_v2) as its inline with other ioctl
  btrfs-control
 The CLI usage/features remains same. However internally the ioctl flag
  is not required to delete all the unmounted devices. Instead leave
  btrfs_ioctl_vol_args::name NULL.

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           | 3 +++
 fs/btrfs/volumes.c         | 9 +++++++++
 fs/btrfs/volumes.h         | 1 +
 include/uapi/linux/btrfs.h | 2 ++
 4 files changed, 15 insertions(+)

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

 cmds-device.c | 63 ++++++++++++++++++++++++++++++++++++++++++++++++++---------
 ioctl.h       |  2 ++
 2 files changed, 56 insertions(+), 9 deletions(-)

[1]
Anand Jain (1):
  fstests: btrfs use forget if not reload

 common/btrfs    | 20 ++++++++++++++++++++
 tests/btrfs/124 |  6 +++---
 tests/btrfs/125 |  6 +++---
 tests/btrfs/154 |  6 +++---
 tests/btrfs/164 |  4 ++--
 5 files changed, 31 insertions(+), 11 deletions(-)

-- 
1.8.3.1

[PATCH RESEND v12] 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, and ::name can be
set to specify the device path. And all unmounted devices can be removed
from the kernel if no device path is provided.

Again, the devices are removed only if the relevant fsid aren't mounted.

This new cli can provide..
 . Release of unwanted btrfs_fs_devices and btrfs_devices memory if the
   device is not going to be mounted.
 . Ability to mount the device in degraded mode when one of the other
   device is corrupted like in split brain raid1.
 . Running test cases which requires btrfs.ko-reload if the rootfs
   is btrfs.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
---
v11->v12: fix coding style add spacing before after ":".
v1->v11: Pls ref to the cover-letter. (sorry about that).

 fs/btrfs/super.c           | 3 +++
 fs/btrfs/volumes.c         | 9 +++++++++
 fs/btrfs/volumes.h         | 1 +
 include/uapi/linux/btrfs.h | 2 ++
 4 files changed, 15 insertions(+)

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index d3c6bbc0aa3a..eba2966913ae 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -2247,6 +2247,9 @@ static long btrfs_control_ioctl(struct file *file, unsigned int cmd,
 		ret = PTR_ERR_OR_ZERO(device);
 		mutex_unlock(&uuid_mutex);
 		break;
+	case BTRFS_IOC_FORGET_DEV:
+		ret = btrfs_forget_devices(vol->name);
+		break;
 	case BTRFS_IOC_DEVICES_READY:
 		mutex_lock(&uuid_mutex);
 		device = btrfs_scan_one_device(vol->name, FMODE_READ,
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 8e36cbb355df..48415a9edd46 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -1397,6 +1397,15 @@ 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(strlen(path) ? path : NULL, 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 1d936ce282c3..a4a89d5050f5 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -414,6 +414,7 @@ int btrfs_open_devices(struct btrfs_fs_devices *fs_devices,
 		       fmode_t flags, void *holder);
 struct btrfs_device *btrfs_scan_one_device(const char *path,
 					   fmode_t flags, void *holder);
+int btrfs_forget_devices(const char *path);
 int btrfs_close_devices(struct btrfs_fs_devices *fs_devices);
 void btrfs_free_extra_devids(struct btrfs_fs_devices *fs_devices, int step);
 void btrfs_assign_next_active_device(struct btrfs_device *device,
diff --git a/include/uapi/linux/btrfs.h b/include/uapi/linux/btrfs.h
index e0763bc4158e..c195896d478f 100644
--- a/include/uapi/linux/btrfs.h
+++ b/include/uapi/linux/btrfs.h
@@ -837,6 +837,8 @@ 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
-- 
1.8.3.1

[PATCH RESEND v12] btrfs-progs: add cli to forget one or all scanned devices

[Anand Jain]

This patch adds cli
  btrfs device forget [dev]
to remove the given device structure in the kernel if the device
is unmounted. 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>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
---
v11->v12: none.
v1->v12: pls ref to the cover-letter.

 cmds-device.c | 72 ++++++++++++++++++++++++++++++++++++++++++++++++-----------
 ioctl.h       |  2 ++
 2 files changed, 61 insertions(+), 13 deletions(-)

diff --git a/cmds-device.c b/cmds-device.c
index 2a05f70a76a9..280d6f555377 100644
--- a/cmds-device.c
+++ b/cmds-device.c
@@ -254,10 +254,32 @@ static int cmd_device_delete(int argc, char **argv)
 	return _cmd_device_remove(argc, argv, cmd_device_delete_usage);
 }
 
+static int btrfs_forget_devices(char *path)
+{
+	struct btrfs_ioctl_vol_args args;
+	int ret;
+	int fd;
+
+	fd = open("/dev/btrfs-control", O_RDWR);
+	if (fd < 0)
+		return -errno;
+
+	memset(&args, 0, sizeof(args));
+	if (path)
+		strncpy_null(args.name, path);
+	ret = ioctl(fd, BTRFS_IOC_FORGET_DEV, &args);
+	if (ret)
+		ret = -errno;
+	close(fd);
+	return ret;
+}
+
 static const char * const cmd_device_scan_usage[] = {
-	"btrfs device scan [(-d|--all-devices)|<device> [<device>...]]",
-	"Scan devices for a btrfs filesystem",
+	"btrfs device scan [(-d|--all-devices)|(-u|--forget)|<device> "\
+							"[<device>...]]",
+	"Scan or forget (deregister) devices for a btrfs filesystem",
 	" -d|--all-devices (deprecated)",
+	" -u|--forget [<device> ..]",
 	NULL
 };
 
@@ -267,37 +289,53 @@ static int cmd_device_scan(int argc, char **argv)
 	int devstart;
 	int all = 0;
 	int ret = 0;
+	int forget = 0;
 
 	optind = 0;
 	while (1) {
 		int c;
 		static const struct option long_options[] = {
 			{ "all-devices", no_argument, NULL, 'd'},
+			{ "forget", no_argument, NULL, 'u'},
 			{ NULL, 0, NULL, 0}
 		};
 
-		c = getopt_long(argc, argv, "d", long_options, NULL);
+		c = getopt_long(argc, argv, "du", long_options, NULL);
 		if (c < 0)
 			break;
 		switch (c) {
 		case 'd':
 			all = 1;
 			break;
+		case 'u':
+			forget = 1;
+			break;
 		default:
 			usage(cmd_device_scan_usage);
 		}
 	}
 	devstart = optind;
 
+	if (all && forget)
+		usage(cmd_device_scan_usage);
+
 	if (all && check_argc_max(argc - optind, 1))
 		usage(cmd_device_scan_usage);
 
 	if (all || argc - optind == 0) {
-		printf("Scanning for Btrfs filesystems\n");
-		ret = btrfs_scan_devices();
-		error_on(ret, "error %d while scanning", ret);
-		ret = btrfs_register_all_devices();
-		error_on(ret, "there are %d errors while registering devices", ret);
+		if (forget) {
+			ret = btrfs_forget_devices(NULL);
+			error_on(ret, "'%s', forget failed",
+				 strerror(-ret));
+		} else {
+			printf("Scanning for Btrfs filesystems\n");
+			ret = btrfs_scan_devices();
+			error_on(ret, "error %d while scanning", ret);
+			ret = btrfs_register_all_devices();
+			error_on(ret,
+				"there are %d errors while registering devices",
+				ret);
+		}
 		goto out;
 	}
 
@@ -315,11 +353,19 @@ static int cmd_device_scan(int argc, char **argv)
 			ret = 1;
 			goto out;
 		}
-		printf("Scanning for Btrfs filesystems in '%s'\n", path);
-		if (btrfs_register_one_device(path) != 0) {
-			ret = 1;
-			free(path);
-			goto out;
+		if (forget) {
+			ret = btrfs_forget_devices(path);
+			if (ret)
+				error("Can't forget '%s': %s",
+							path, strerror(-ret));
+		} else {
+			printf("Scanning for Btrfs filesystems in '%s'\n",
+									path);
+			if (btrfs_register_one_device(path) != 0) {
+				ret = 1;
+				free(path);
+				goto out;
+			}
 		}
 		free(path);
 	}
diff --git a/ioctl.h b/ioctl.h
index 709e996f401c..e27d80e09392 100644
--- a/ioctl.h
+++ b/ioctl.h
@@ -721,6 +721,8 @@ 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
-- 
1.8.3.1

[PATCH RESEND] fstests: btrfs use forget if not reload

[Anand Jain]

[I will send this the xfstest ML after kernel and progs patch
 has been integrated].

btrfs reload was introduced to cleanup the device list inside the btrfs
kernel module.

The problem with the reload approach is that you can't run btrfs test
cases 124,125, 154 and 164 on the system with btrfs as root fs.

Now as we are introducing the btrfs forget feature as an btrfs device
scan option [1], so here are its pertaining changes in the fstests.

So these changes ensures we use the forget feature where available and
if its not then falls back to the reload approach.

[1]
btrfs-progs: add cli to forget one or all scanned devices
btrfs: introduce feature to forget a btrfs device

Signed-off-by: Anand Jain <anand.jain@oracle.com>
---
 common/btrfs    | 20 ++++++++++++++++++++
 tests/btrfs/124 |  6 +++---
 tests/btrfs/125 |  6 +++---
 tests/btrfs/154 |  6 +++---
 tests/btrfs/164 |  4 ++--
 5 files changed, 31 insertions(+), 11 deletions(-)

diff --git a/common/btrfs b/common/btrfs
index 26dc0bb9600f..c7fbec11c8c1 100644
--- a/common/btrfs
+++ b/common/btrfs
@@ -374,3 +374,23 @@ _scratch_btrfs_sectorsize()
 	$BTRFS_UTIL_PROG inspect-internal dump-super $SCRATCH_DEV |\
 		grep sectorsize | awk '{print $2}'
 }
+
+_btrfs_supports_forget()
+{
+	$BTRFS_UTIL_PROG device scan --help | grep -wq forget && \
+		$BTRFS_UTIL_PROG device scan --forget > /dev/null 2>&1
+}
+
+_require_btrfs_forget_if_not_fs_loadable()
+{
+	_btrfs_supports_forget && return
+
+	_require_loadable_fs_module "btrfs"
+}
+
+_btrfs_forget_if_not_fs_reload()
+{
+	_btrfs_supports_forget && return
+
+	_reload_fs_module "btrfs"
+}
diff --git a/tests/btrfs/124 b/tests/btrfs/124
index ce3ad6aa3a58..edbeff1443f5 100755
--- a/tests/btrfs/124
+++ b/tests/btrfs/124
@@ -51,7 +51,7 @@ _supported_fs btrfs
 _supported_os Linux
 _require_scratch_dev_pool 2
 _test_unmount
-_require_loadable_fs_module "btrfs"
+_require_btrfs_forget_if_not_fs_loadable
 
 _scratch_dev_pool_get 2
 
@@ -86,7 +86,7 @@ echo "clean btrfs ko" >> $seqres.full
 _scratch_unmount
 
 # un-scan the btrfs devices
-_reload_fs_module "btrfs"
+_btrfs_forget_if_not_fs_reload
 
 echo >> $seqres.full
 echo "-----Write degraded mount fill upto $max_fs_sz bytes-----" >> $seqres.full
@@ -125,7 +125,7 @@ echo
 echo "Mount degraded with the other dev"
 _scratch_unmount
 # un-scan the btrfs devices
-_reload_fs_module "btrfs"
+_btrfs_forget_if_not_fs_reload
 _mount -o degraded $dev2 $SCRATCH_MNT >>$seqres.full 2>&1
 _run_btrfs_util_prog filesystem show
 checkpoint3=`md5sum $SCRATCH_MNT/tf2`
diff --git a/tests/btrfs/125 b/tests/btrfs/125
index e38de264b28e..9161a2ddeaad 100755
--- a/tests/btrfs/125
+++ b/tests/btrfs/125
@@ -50,7 +50,7 @@ _supported_fs btrfs
 _supported_os Linux
 _require_scratch_dev_pool 3
 _test_unmount
-_require_loadable_fs_module "btrfs"
+_require_btrfs_forget_if_not_fs_loadable
 
 _scratch_dev_pool_get 3
 
@@ -102,7 +102,7 @@ echo "unmount" >> $seqres.full
 _scratch_unmount
 echo "clean btrfs ko" >> $seqres.full
 # un-scan the btrfs devices
-_reload_fs_module "btrfs"
+_btrfs_forget_if_not_fs_reload
 _mount -o degraded,device=$dev2 $dev1 $SCRATCH_MNT >>$seqres.full 2>&1
 dd if=/dev/zero of="$SCRATCH_MNT"/tf2 bs=$bs count=$count \
 					>>$seqres.full 2>&1
@@ -138,7 +138,7 @@ echo "Mount degraded but with other dev"
 
 _scratch_unmount
 # un-scan the btrfs devices
-_reload_fs_module "btrfs"
+_btrfs_forget_if_not_fs_reload
 
 _mount -o degraded,device=${dev2} $dev3 $SCRATCH_MNT >>$seqres.full 2>&1
 
diff --git a/tests/btrfs/154 b/tests/btrfs/154
index 99ea232aba4c..01745d20e9fc 100755
--- a/tests/btrfs/154
+++ b/tests/btrfs/154
@@ -36,7 +36,7 @@ rm -f $seqres.full
 _supported_fs btrfs
 _supported_os Linux
 _require_scratch_dev_pool 2
-_require_loadable_fs_module "btrfs"
+_require_btrfs_forget_if_not_fs_loadable
 
 _scratch_dev_pool_get 2
 
@@ -90,7 +90,7 @@ degrade_mount_write()
 
 	echo "clean btrfs ko" >> $seqres.full
 	# un-scan the btrfs devices
-	_reload_fs_module "btrfs"
+	_btrfs_forget_if_not_fs_reload
 	_mount -o degraded $DEV1 $SCRATCH_MNT >>$seqres.full 2>&1
 	cnt=$(( $COUNT/10 ))
 	dd if=/dev/urandom of="$SCRATCH_MNT"/tf1 bs=$bs count=$cnt \
@@ -142,7 +142,7 @@ verify()
 	echo "unmount" >> $seqres.full
 
 	_scratch_unmount
-	_reload_fs_module "btrfs"
+	_btrfs_forget_if_not_fs_reload
 	_mount -o degraded $DEV2 $SCRATCH_MNT >>$seqres.full 2>&1
 	verify_checkpoint1=`md5sum $SCRATCH_MNT/tf1`
 	verify_checkpoint2=`md5sum $SCRATCH_MNT/tf2`
diff --git a/tests/btrfs/164 b/tests/btrfs/164
index 097191a0e493..55042c4035e0 100755
--- a/tests/btrfs/164
+++ b/tests/btrfs/164
@@ -36,7 +36,7 @@ rm -f $seqres.full
 # Modify as appropriate.
 _supported_fs btrfs
 _supported_os Linux
-_require_loadable_fs_module "btrfs"
+_require_btrfs_forget_if_not_fs_loadable
 _require_scratch_dev_pool 2
 
 _scratch_dev_pool_get 2
@@ -69,7 +69,7 @@ delete_seed()
 {
 	_run_btrfs_util_prog device delete $dev_seed $SCRATCH_MNT
 	_scratch_unmount
-	_reload_fs_module "btrfs"
+	_btrfs_forget_if_not_fs_reload
 	run_check _mount $dev_sprout $SCRATCH_MNT
 	_run_btrfs_util_prog filesystem show -m $SCRATCH_MNT
 	echo -- sprout --
-- 
1.8.3.1

Re: [PATCH RESEND v12] btrfs: introduce feature to forget a btrfs device

[David Sterba]

On Thu, Jan 03, 2019 at 03:54:26PM +0800, Anand Jain wrote:
> > I think this should reflect the status of the operation. The ioctl
> > caller has no information about success/error. Eg. an invalid device
> > path passed could return -ENOENT, 0 if it was released and 1 if not.
> > 
> > In case of all devices, it's probably ok to return 0.
> 
> OK. v13 will return error if the given device is not found,
> and I find ENXIO is more suitable (instead of ENOENT).
> If you disagree pls can you make the changes as in [1]
> when integrating. I have tested with both.

ENXIO refers to device nodes, however for paths it should be ok to use
ENOENT, same what would eg. stat return on the given device path.

The ENXIO is used for lseek and is documented as such, I'd rather stick
to semantics of 'file' even though it's a path to a device.

Re: [PATCH RESEND v12] btrfs: introduce feature to forget a btrfs device

[Anand Jain]

On 01/03/2019 12:00 AM, David Sterba wrote:
> On Wed, Jan 02, 2019 at 01:49:31PM +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.
>>
>> The argument it takes is struct btrfs_ioctl_vol_args, and ::name can be
>> set to specify the device path. And all unmounted devices can be removed
>> from the kernel if no device path is provided.
>>
>> Again, the devices are removed only if the relevant fsid aren't mounted.
>>
>> This new cli can provide..
>>   . Release of unwanted btrfs_fs_devices and btrfs_devices memory if the
>>     device is not going to be mounted.
>>   . Ability to mount the device in degraded mode when one of the other
>>     device is corrupted like in split brain raid1.
>>   . Running test cases which requires btrfs.ko-reload if the rootfs
>>     is btrfs.
>>
>> Signed-off-by: Anand Jain <anand.jain@oracle.com>
>> Reviewed-by: Nikolay Borisov <nborisov@suse.com>
>> ---
>> v11->v12: fix coding style add spacing before after ":".
>> v1->v11: Pls ref to the cover-letter. (sorry about that).
>>
>>   fs/btrfs/super.c           | 3 +++
>>   fs/btrfs/volumes.c         | 9 +++++++++
>>   fs/btrfs/volumes.h         | 1 +
>>   include/uapi/linux/btrfs.h | 2 ++
>>   4 files changed, 15 insertions(+)
>>
>> diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
>> index d3c6bbc0aa3a..eba2966913ae 100644
>> --- a/fs/btrfs/super.c
>> +++ b/fs/btrfs/super.c
>> @@ -2247,6 +2247,9 @@ static long btrfs_control_ioctl(struct file *file, unsigned int cmd,
>>   		ret = PTR_ERR_OR_ZERO(device);
>>   		mutex_unlock(&uuid_mutex);
>>   		break;
>> +	case BTRFS_IOC_FORGET_DEV:
>> +		ret = btrfs_forget_devices(vol->name);
>> +		break;
>>   	case BTRFS_IOC_DEVICES_READY:
>>   		mutex_lock(&uuid_mutex);
>>   		device = btrfs_scan_one_device(vol->name, FMODE_READ,
>> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
>> index 8e36cbb355df..48415a9edd46 100644
>> --- a/fs/btrfs/volumes.c
>> +++ b/fs/btrfs/volumes.c
>> @@ -1397,6 +1397,15 @@ 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(strlen(path) ? path : NULL, NULL);
>> +	mutex_unlock(&uuid_mutex);
>> +
>> +	return 0;
> 
> I think this should reflect the status of the operation. The ioctl
> caller has no information about success/error. Eg. an invalid device
> path passed could return -ENOENT, 0 if it was released and 1 if not.
> 
> In case of all devices, it's probably ok to return 0.


OK. v13 will return error if the given device is not found,
and I find ENXIO is more suitable (instead of ENOENT).
If you disagree pls can you make the changes as in [1]
when integrating. I have tested with both.

--------
[1]
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 2ab42bfe5d3c..e04784c64a98 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -763,7 +763,7 @@ static int btrfs_free_stale_devices(const char *path,
         int ret;

         if (path)
-               ret = -ENXIO;
+               ret = -ENOENT;
         else
                 ret = 0;
----------------

Thanks, Anand

Re: [PATCH RESEND v12] btrfs: introduce feature to forget a btrfs device

[David Sterba]

On Wed, Jan 02, 2019 at 01:49:31PM +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.
> 
> The argument it takes is struct btrfs_ioctl_vol_args, and ::name can be
> set to specify the device path. And all unmounted devices can be removed
> from the kernel if no device path is provided.
> 
> Again, the devices are removed only if the relevant fsid aren't mounted.
> 
> This new cli can provide..
>  . Release of unwanted btrfs_fs_devices and btrfs_devices memory if the
>    device is not going to be mounted.
>  . Ability to mount the device in degraded mode when one of the other
>    device is corrupted like in split brain raid1.
>  . Running test cases which requires btrfs.ko-reload if the rootfs
>    is btrfs.
> 
> Signed-off-by: Anand Jain <anand.jain@oracle.com>
> Reviewed-by: Nikolay Borisov <nborisov@suse.com>
> ---
> v11->v12: fix coding style add spacing before after ":".
> v1->v11: Pls ref to the cover-letter. (sorry about that).
> 
>  fs/btrfs/super.c           | 3 +++
>  fs/btrfs/volumes.c         | 9 +++++++++
>  fs/btrfs/volumes.h         | 1 +
>  include/uapi/linux/btrfs.h | 2 ++
>  4 files changed, 15 insertions(+)
> 
> diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
> index d3c6bbc0aa3a..eba2966913ae 100644
> --- a/fs/btrfs/super.c
> +++ b/fs/btrfs/super.c
> @@ -2247,6 +2247,9 @@ static long btrfs_control_ioctl(struct file *file, unsigned int cmd,
>  		ret = PTR_ERR_OR_ZERO(device);
>  		mutex_unlock(&uuid_mutex);
>  		break;
> +	case BTRFS_IOC_FORGET_DEV:
> +		ret = btrfs_forget_devices(vol->name);
> +		break;
>  	case BTRFS_IOC_DEVICES_READY:
>  		mutex_lock(&uuid_mutex);
>  		device = btrfs_scan_one_device(vol->name, FMODE_READ,
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index 8e36cbb355df..48415a9edd46 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -1397,6 +1397,15 @@ 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(strlen(path) ? path : NULL, NULL);
> +	mutex_unlock(&uuid_mutex);
> +
> +	return 0;

I think this should reflect the status of the operation. The ioctl
caller has no information about success/error. Eg. an invalid device
path passed could return -ENOENT, 0 if it was released and 1 if not.

In case of all devices, it's probably ok to return 0.

[PATCH RESEND v12] 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, and ::name can be
set to specify the device path. And all unmounted devices can be removed
from the kernel if no device path is provided.

Again, the devices are removed only if the relevant fsid aren't mounted.

This new cli can provide..
 . Release of unwanted btrfs_fs_devices and btrfs_devices memory if the
   device is not going to be mounted.
 . Ability to mount the device in degraded mode when one of the other
   device is corrupted like in split brain raid1.
 . Running test cases which requires btrfs.ko-reload if the rootfs
   is btrfs.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
---
v11->v12: fix coding style add spacing before after ":".
v1->v11: Pls ref to the cover-letter. (sorry about that).

 fs/btrfs/super.c           | 3 +++
 fs/btrfs/volumes.c         | 9 +++++++++
 fs/btrfs/volumes.h         | 1 +
 include/uapi/linux/btrfs.h | 2 ++
 4 files changed, 15 insertions(+)

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index d3c6bbc0aa3a..eba2966913ae 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -2247,6 +2247,9 @@ static long btrfs_control_ioctl(struct file *file, unsigned int cmd,
 		ret = PTR_ERR_OR_ZERO(device);
 		mutex_unlock(&uuid_mutex);
 		break;
+	case BTRFS_IOC_FORGET_DEV:
+		ret = btrfs_forget_devices(vol->name);
+		break;
 	case BTRFS_IOC_DEVICES_READY:
 		mutex_lock(&uuid_mutex);
 		device = btrfs_scan_one_device(vol->name, FMODE_READ,
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 8e36cbb355df..48415a9edd46 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -1397,6 +1397,15 @@ 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(strlen(path) ? path : NULL, 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 1d936ce282c3..a4a89d5050f5 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -414,6 +414,7 @@ int btrfs_open_devices(struct btrfs_fs_devices *fs_devices,
 		       fmode_t flags, void *holder);
 struct btrfs_device *btrfs_scan_one_device(const char *path,
 					   fmode_t flags, void *holder);
+int btrfs_forget_devices(const char *path);
 int btrfs_close_devices(struct btrfs_fs_devices *fs_devices);
 void btrfs_free_extra_devids(struct btrfs_fs_devices *fs_devices, int step);
 void btrfs_assign_next_active_device(struct btrfs_device *device,
diff --git a/include/uapi/linux/btrfs.h b/include/uapi/linux/btrfs.h
index e0763bc4158e..c195896d478f 100644
--- a/include/uapi/linux/btrfs.h
+++ b/include/uapi/linux/btrfs.h
@@ -837,6 +837,8 @@ 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
-- 
1.8.3.1

[PATCH RESEND v12] 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, and ::name can be
set to specify the device path. And all unmounted devices can be removed
from the kernel if no device path is provided.

Again, the devices are removed only if the relevant fsid aren't mounted.

This new cli can provide..
 . Release of unwanted btrfs_fs_devices and btrfs_devices memory if the
   device is not going to be mounted.
 . Ability to mount the device in degraded mode when one of the other
   device is corrupted like in split brain raid1.
 . Running test cases which requires btrfs.ko-reload if the rootfs
   is btrfs.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
---
v11->v12: fix coding style add spacing before after ":".
v1->v11: Pls ref to the cover-letter. (sorry about that).

 fs/btrfs/super.c           | 3 +++
 fs/btrfs/volumes.c         | 9 +++++++++
 fs/btrfs/volumes.h         | 1 +
 include/uapi/linux/btrfs.h | 2 ++
 4 files changed, 15 insertions(+)

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index d3c6bbc0aa3a..eba2966913ae 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -2247,6 +2247,9 @@ static long btrfs_control_ioctl(struct file *file, unsigned int cmd,
 		ret = PTR_ERR_OR_ZERO(device);
 		mutex_unlock(&uuid_mutex);
 		break;
+	case BTRFS_IOC_FORGET_DEV:
+		ret = btrfs_forget_devices(vol->name);
+		break;
 	case BTRFS_IOC_DEVICES_READY:
 		mutex_lock(&uuid_mutex);
 		device = btrfs_scan_one_device(vol->name, FMODE_READ,
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 8e36cbb355df..48415a9edd46 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -1397,6 +1397,15 @@ 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(strlen(path) ? path : NULL, 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 1d936ce282c3..a4a89d5050f5 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -414,6 +414,7 @@ int btrfs_open_devices(struct btrfs_fs_devices *fs_devices,
 		       fmode_t flags, void *holder);
 struct btrfs_device *btrfs_scan_one_device(const char *path,
 					   fmode_t flags, void *holder);
+int btrfs_forget_devices(const char *path);
 int btrfs_close_devices(struct btrfs_fs_devices *fs_devices);
 void btrfs_free_extra_devids(struct btrfs_fs_devices *fs_devices, int step);
 void btrfs_assign_next_active_device(struct btrfs_device *device,
diff --git a/include/uapi/linux/btrfs.h b/include/uapi/linux/btrfs.h
index e0763bc4158e..c195896d478f 100644
--- a/include/uapi/linux/btrfs.h
+++ b/include/uapi/linux/btrfs.h
@@ -837,6 +837,8 @@ 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
-- 
1.8.3.1