| Message ID | 7df68f272490c55349b44a33dd7ac19ccf87560f.1634598572.git.anand.jain@oracle.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | provide fsid in sysfs devinfo | expand |
On Tue, Oct 19, 2021 at 08:22:10AM +0800, Anand Jain wrote: > In the case of the seed device, the fsid can be different from the mounted > sprout fsid. The userland has to read the device superblock to know the > fsid but, that idea fails if the device is missing. So add a sysfs > interface devinfo/<devid>/fsid to show the fsid of the device. > > For example: > $ cd /sys/fs/btrfs/b10b02a5-f9de-4276-b9e8-2bfd09a578a8 > > $ cat devinfo/1/fsid > c44d771f-639d-4df3-99ec-5bc7ad2af93b > $ cat devinfo/3/fsid > b10b02a5-f9de-4276-b9e8-2bfd09a578a8 How do you create such setup? I can't reproduce it. The simplest seeding: mkfs.btrfs /dev/sdx btrfstune -S 1 /dev/sdx mount /dev/sdx mnt ... the device has the same FSID as is the sysfs directory name With a new device and removed the seeding one: btrfs device add /dev/sdy mnt mount -o remount,rw mnt btrfs device delete /dev/sdx mnt ... both devices have the same fsid as well
On 21/10/2021 02:59, David Sterba wrote: > On Tue, Oct 19, 2021 at 08:22:10AM +0800, Anand Jain wrote: >> In the case of the seed device, the fsid can be different from the mounted >> sprout fsid. The userland has to read the device superblock to know the >> fsid but, that idea fails if the device is missing. So add a sysfs >> interface devinfo/<devid>/fsid to show the fsid of the device. >> >> For example: >> $ cd /sys/fs/btrfs/b10b02a5-f9de-4276-b9e8-2bfd09a578a8 >> >> $ cat devinfo/1/fsid >> c44d771f-639d-4df3-99ec-5bc7ad2af93b >> $ cat devinfo/3/fsid >> b10b02a5-f9de-4276-b9e8-2bfd09a578a8 > > How do you create such setup? I can't reproduce it. > > The simplest seeding: > > mkfs.btrfs /dev/sdx > btrfstune -S 1 /dev/sdx > mount /dev/sdx mnt > ... the device has the same FSID as is the sysfs directory name > > With a new device and removed the seeding one: > > btrfs device add /dev/sdy mnt At this step, we generate a new fsid for the writeable FS. Let's call it sprout-fsid. (If you check the sys-fs fsid, you will have two fsid here). Also, at this step, the fs_info->fs_devices->fsid changes from seed-fsid to the sprout-fsid. So, we should make the <mnt> also a writeable without the need to call 'remount,rw' explicitly IMO. What do you think? > mount -o remount,rw mnt > btrfs device delete /dev/sdx mnt > ... both devices have the same fsid as well Thanks, Anand
On 21/10/2021 12:03, Anand Jain wrote: > On 21/10/2021 02:59, David Sterba wrote: >> On Tue, Oct 19, 2021 at 08:22:10AM +0800, Anand Jain wrote: >>> In the case of the seed device, the fsid can be different from the >>> mounted >>> sprout fsid. The userland has to read the device superblock to know the >>> fsid but, that idea fails if the device is missing. So add a sysfs >>> interface devinfo/<devid>/fsid to show the fsid of the device. >>> >>> For example: >>> $ cd /sys/fs/btrfs/b10b02a5-f9de-4276-b9e8-2bfd09a578a8 >>> >>> $ cat devinfo/1/fsid >>> c44d771f-639d-4df3-99ec-5bc7ad2af93b >>> $ cat devinfo/3/fsid >>> b10b02a5-f9de-4276-b9e8-2bfd09a578a8 >> >> How do you create such setup? I can't reproduce it. >> >> The simplest seeding: >> >> mkfs.btrfs /dev/sdx >> btrfstune -S 1 /dev/sdx >> mount /dev/sdx mnt >> ... the device has the same FSID as is the sysfs directory name >> >> With a new device and removed the seeding one: >> >> btrfs device add /dev/sdy mnt > > At this step, we generate a new fsid for the writeable FS. Let's call > it sprout-fsid. (If you check the sys-fs fsid, you will have two fsid > here). > > Also, at this step, > the > fs_info->fs_devices->fsid > changes from seed-fsid to the sprout-fsid. > So, we should make the <mnt> also a writeable without the need to call > 'remount,rw' explicitly IMO. What do you think? > More importantly, the fs_info->super_copy is of sprout device. So there isn't any reason that we should maintain the new sprout fs as readonly after the device add. >> mount -o remount,rw mnt >> btrfs device delete /dev/sdx mnt >> ... both devices have the same fsid as well > > > Thanks, Anand > > > >
diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c index c0ea7269ff57..c10fc39cb677 100644 --- a/fs/btrfs/sysfs.c +++ b/fs/btrfs/sysfs.c @@ -1538,6 +1538,16 @@ static ssize_t btrfs_devinfo_writeable_show(struct kobject *kobj, } BTRFS_ATTR(devid, writeable, btrfs_devinfo_writeable_show); +static ssize_t btrfs_devinfo_fsid_show(struct kobject *kobj, + struct kobj_attribute *a, char *buf) +{ + struct btrfs_device *device = container_of(kobj, struct btrfs_device, + devid_kobj); + + return sysfs_emit(buf, "%pU\n", device->fs_devices->fsid); +} +BTRFS_ATTR(devid, fsid, btrfs_devinfo_fsid_show); + static ssize_t btrfs_devinfo_error_stats_show(struct kobject *kobj, struct kobj_attribute *a, char *buf) { @@ -1578,6 +1588,7 @@ static struct attribute *devid_attrs[] = { BTRFS_ATTR_PTR(devid, replace_target), BTRFS_ATTR_PTR(devid, scrub_speed_max), BTRFS_ATTR_PTR(devid, writeable), + BTRFS_ATTR_PTR(devid, fsid), NULL }; ATTRIBUTE_GROUPS(devid);
In the case of the seed device, the fsid can be different from the mounted sprout fsid. The userland has to read the device superblock to know the fsid but, that idea fails if the device is missing. So add a sysfs interface devinfo/<devid>/fsid to show the fsid of the device. For example: $ cd /sys/fs/btrfs/b10b02a5-f9de-4276-b9e8-2bfd09a578a8 $ cat devinfo/1/fsid c44d771f-639d-4df3-99ec-5bc7ad2af93b $ cat devinfo/3/fsid b10b02a5-f9de-4276-b9e8-2bfd09a578a8 Signed-off-by: Anand Jain <anand.jain@oracle.com> --- fs/btrfs/sysfs.c | 11 +++++++++++ 1 file changed, 11 insertions(+)