* [PATCH] btrfs: track exclusive filesystem operation in flags
@ 2017-03-28 12:44 David Sterba
2017-03-29 10:01 ` Anand Jain
0 siblings, 1 reply; 3+ messages in thread
From: David Sterba @ 2017-03-28 12:44 UTC (permalink / raw)
To: linux-btrfs; +Cc: David Sterba
There are several operations, usually started from ioctls, that cannot
run concurrently. The status is tracked in
mutually_exclusive_operation_running as an atomic_t. We can easily track
the status as one of the per-filesystem flag bits with same
synchronization guarantees.
The conversion replaces:
* atomic_xchg(..., 1) -> test_and_set_bit(FLAG, ...)
* atomic_set(..., 0) -> clear_bit(FLAG, ...)
Signed-off-by: David Sterba <dsterba@suse.com>
---
fs/btrfs/ctree.h | 7 +++++--
fs/btrfs/dev-replace.c | 5 ++---
fs/btrfs/ioctl.c | 33 +++++++++++++++------------------
fs/btrfs/volumes.c | 6 +++---
4 files changed, 25 insertions(+), 26 deletions(-)
diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 29b7fc28c607..2521752c4e4a 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -702,6 +702,11 @@ struct btrfs_delayed_root;
#define BTRFS_FS_BTREE_ERR 11
#define BTRFS_FS_LOG1_ERR 12
#define BTRFS_FS_LOG2_ERR 13
+/*
+ * Indicate that a whole-filesystem exclusive operation is running
+ * (device replace, resize, device add/delete, balance)
+ */
+#define BTRFS_FS_EXCL_OP 14
struct btrfs_fs_info {
u8 fsid[BTRFS_FSID_SIZE];
@@ -1067,8 +1072,6 @@ struct btrfs_fs_info {
/* device replace state */
struct btrfs_dev_replace dev_replace;
- atomic_t mutually_exclusive_operation_running;
-
struct percpu_counter bio_counter;
wait_queue_head_t replace_wait;
diff --git a/fs/btrfs/dev-replace.c b/fs/btrfs/dev-replace.c
index e653921f05d9..de7b2c897fe0 100644
--- a/fs/btrfs/dev-replace.c
+++ b/fs/btrfs/dev-replace.c
@@ -784,8 +784,7 @@ int btrfs_resume_dev_replace_async(struct btrfs_fs_info *fs_info)
}
btrfs_dev_replace_unlock(dev_replace, 1);
- WARN_ON(atomic_xchg(
- &fs_info->mutually_exclusive_operation_running, 1));
+ WARN_ON(test_and_set_bit(BTRFS_FS_EXCL_OP, &fs_info->flags));
task = kthread_run(btrfs_dev_replace_kthread, fs_info, "btrfs-devrepl");
return PTR_ERR_OR_ZERO(task);
}
@@ -814,7 +813,7 @@ static int btrfs_dev_replace_kthread(void *data)
(unsigned int)progress);
}
btrfs_dev_replace_continue_on_mount(fs_info);
- atomic_set(&fs_info->mutually_exclusive_operation_running, 0);
+ clear_bit(BTRFS_FS_EXCL_OP, &fs_info->flags);
return 0;
}
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index dabfc7ac48a6..a29dc3fd7152 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -1504,7 +1504,7 @@ static noinline int btrfs_ioctl_resize(struct file *file,
if (ret)
return ret;
- if (atomic_xchg(&fs_info->mutually_exclusive_operation_running, 1)) {
+ if (test_and_set_bit(BTRFS_FS_EXCL_OP, &fs_info->flags)) {
mnt_drop_write_file(file);
return BTRFS_ERROR_DEV_EXCL_RUN_IN_PROGRESS;
}
@@ -1619,7 +1619,7 @@ static noinline int btrfs_ioctl_resize(struct file *file,
kfree(vol_args);
out:
mutex_unlock(&fs_info->volume_mutex);
- atomic_set(&fs_info->mutually_exclusive_operation_running, 0);
+ clear_bit(BTRFS_FS_EXCL_OP, &fs_info->flags);
mnt_drop_write_file(file);
return ret;
}
@@ -2661,7 +2661,7 @@ static long btrfs_ioctl_add_dev(struct btrfs_fs_info *fs_info, void __user *arg)
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
- if (atomic_xchg(&fs_info->mutually_exclusive_operation_running, 1))
+ if (test_and_set_bit(BTRFS_FS_EXCL_OP, &fs_info->flags))
return BTRFS_ERROR_DEV_EXCL_RUN_IN_PROGRESS;
mutex_lock(&fs_info->volume_mutex);
@@ -2680,7 +2680,7 @@ static long btrfs_ioctl_add_dev(struct btrfs_fs_info *fs_info, void __user *arg)
kfree(vol_args);
out:
mutex_unlock(&fs_info->volume_mutex);
- atomic_set(&fs_info->mutually_exclusive_operation_running, 0);
+ clear_bit(BTRFS_FS_EXCL_OP, &fs_info->flags);
return ret;
}
@@ -2708,7 +2708,7 @@ static long btrfs_ioctl_rm_dev_v2(struct file *file, void __user *arg)
if (vol_args->flags & ~BTRFS_VOL_ARG_V2_FLAGS_SUPPORTED)
return -EOPNOTSUPP;
- if (atomic_xchg(&fs_info->mutually_exclusive_operation_running, 1)) {
+ if (test_and_set_bit(BTRFS_FS_EXCL_OP, &fs_info->flags)) {
ret = BTRFS_ERROR_DEV_EXCL_RUN_IN_PROGRESS;
goto out;
}
@@ -2721,7 +2721,7 @@ static long btrfs_ioctl_rm_dev_v2(struct file *file, void __user *arg)
ret = btrfs_rm_device(fs_info, vol_args->name, 0);
}
mutex_unlock(&fs_info->volume_mutex);
- atomic_set(&fs_info->mutually_exclusive_operation_running, 0);
+ clear_bit(BTRFS_FS_EXCL_OP, &fs_info->flags);
if (!ret) {
if (vol_args->flags & BTRFS_DEVICE_SPEC_BY_ID)
@@ -2752,7 +2752,7 @@ static long btrfs_ioctl_rm_dev(struct file *file, void __user *arg)
if (ret)
return ret;
- if (atomic_xchg(&fs_info->mutually_exclusive_operation_running, 1)) {
+ if (test_and_set_bit(BTRFS_FS_EXCL_OP, &fs_info->flags)) {
ret = BTRFS_ERROR_DEV_EXCL_RUN_IN_PROGRESS;
goto out_drop_write;
}
@@ -2772,7 +2772,7 @@ static long btrfs_ioctl_rm_dev(struct file *file, void __user *arg)
btrfs_info(fs_info, "disk deleted %s", vol_args->name);
kfree(vol_args);
out:
- atomic_set(&fs_info->mutually_exclusive_operation_running, 0);
+ clear_bit(BTRFS_FS_EXCL_OP, &fs_info->flags);
out_drop_write:
mnt_drop_write_file(file);
@@ -4442,13 +4442,11 @@ static long btrfs_ioctl_dev_replace(struct btrfs_fs_info *fs_info,
ret = -EROFS;
goto out;
}
- if (atomic_xchg(
- &fs_info->mutually_exclusive_operation_running, 1)) {
+ if (test_and_set_bit(BTRFS_FS_EXCL_OP, &fs_info->flags)) {
ret = BTRFS_ERROR_DEV_EXCL_RUN_IN_PROGRESS;
} else {
ret = btrfs_dev_replace_by_ioctl(fs_info, p);
- atomic_set(
- &fs_info->mutually_exclusive_operation_running, 0);
+ clear_bit(BTRFS_FS_EXCL_OP, &fs_info->flags);
}
break;
case BTRFS_IOCTL_DEV_REPLACE_CMD_STATUS:
@@ -4643,7 +4641,7 @@ static long btrfs_ioctl_balance(struct file *file, void __user *arg)
return ret;
again:
- if (!atomic_xchg(&fs_info->mutually_exclusive_operation_running, 1)) {
+ if (!test_and_set_bit(BTRFS_FS_EXCL_OP, &fs_info->flags)) {
mutex_lock(&fs_info->volume_mutex);
mutex_lock(&fs_info->balance_mutex);
need_unlock = true;
@@ -4689,7 +4687,7 @@ static long btrfs_ioctl_balance(struct file *file, void __user *arg)
}
locked:
- BUG_ON(!atomic_read(&fs_info->mutually_exclusive_operation_running));
+ BUG_ON(!test_bit(BTRFS_FS_EXCL_OP, &fs_info->flags));
if (arg) {
bargs = memdup_user(arg, sizeof(*bargs));
@@ -4745,11 +4743,10 @@ static long btrfs_ioctl_balance(struct file *file, void __user *arg)
do_balance:
/*
- * Ownership of bctl and mutually_exclusive_operation_running
+ * Ownership of bctl and filesystem flag BTRFS_FS_EXCL_OP
* goes to to btrfs_balance. bctl is freed in __cancel_balance,
* or, if restriper was paused all the way until unmount, in
- * free_fs_info. mutually_exclusive_operation_running is
- * cleared in __cancel_balance.
+ * free_fs_info. The flag is cleared in __cancel_balance.
*/
need_unlock = false;
@@ -4769,7 +4766,7 @@ static long btrfs_ioctl_balance(struct file *file, void __user *arg)
mutex_unlock(&fs_info->balance_mutex);
mutex_unlock(&fs_info->volume_mutex);
if (need_unlock)
- atomic_set(&fs_info->mutually_exclusive_operation_running, 0);
+ clear_bit(BTRFS_FS_EXCL_OP, &fs_info->flags);
out:
mnt_drop_write_file(file);
return ret;
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 73d56eef5e60..91580cf471e4 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -3736,7 +3736,7 @@ static void __cancel_balance(struct btrfs_fs_info *fs_info)
if (ret)
btrfs_handle_fs_error(fs_info, ret, NULL);
- atomic_set(&fs_info->mutually_exclusive_operation_running, 0);
+ clear_bit(BTRFS_FS_EXCL_OP, &fs_info->flags);
}
/* Non-zero return value signifies invalidity */
@@ -3910,7 +3910,7 @@ int btrfs_balance(struct btrfs_balance_control *bctl,
__cancel_balance(fs_info);
else {
kfree(bctl);
- atomic_set(&fs_info->mutually_exclusive_operation_running, 0);
+ clear_bit(BTRFS_FS_EXCL_OP, &fs_info->flags);
}
return ret;
}
@@ -4000,7 +4000,7 @@ int btrfs_recover_balance(struct btrfs_fs_info *fs_info)
btrfs_balance_sys(leaf, item, &disk_bargs);
btrfs_disk_balance_args_to_cpu(&bctl->sys, &disk_bargs);
- WARN_ON(atomic_xchg(&fs_info->mutually_exclusive_operation_running, 1));
+ WARN_ON(test_and_set_bit(BTRFS_FS_EXCL_OP, &fs_info->flags));
mutex_lock(&fs_info->volume_mutex);
mutex_lock(&fs_info->balance_mutex);
--
2.12.0
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] btrfs: track exclusive filesystem operation in flags
2017-03-28 12:44 [PATCH] btrfs: track exclusive filesystem operation in flags David Sterba
@ 2017-03-29 10:01 ` Anand Jain
2017-03-29 13:21 ` David Sterba
0 siblings, 1 reply; 3+ messages in thread
From: Anand Jain @ 2017-03-29 10:01 UTC (permalink / raw)
To: David Sterba, linux-btrfs
On 03/28/2017 08:44 PM, David Sterba wrote:
> There are several operations, usually started from ioctls, that cannot
> run concurrently. The status is tracked in
> mutually_exclusive_operation_running as an atomic_t. We can easily track
> the status as one of the per-filesystem flag bits with same
> synchronization guarantees.
>
> The conversion replaces:
>
> * atomic_xchg(..., 1) -> test_and_set_bit(FLAG, ...)
> * atomic_set(..., 0) -> clear_bit(FLAG, ...)
Makes sense.
Reviewed-by: Anand Jain <anand.jain@oracle.com>
However in the long term do you think its better to have
BTRFS_FS_EXCL_OP flag in the struct btrfs_fs_devices
rather than in struct btrfs_fs_info ? because we don't have
fs_info until device is mounted and in the long term we could
have a feature where volume can be maintained just after the
device scan without device being mounted.
Thanks, Anand
> Signed-off-by: David Sterba <dsterba@suse.com>
> ---
> fs/btrfs/ctree.h | 7 +++++--
> fs/btrfs/dev-replace.c | 5 ++---
> fs/btrfs/ioctl.c | 33 +++++++++++++++------------------
> fs/btrfs/volumes.c | 6 +++---
> 4 files changed, 25 insertions(+), 26 deletions(-)
>
> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
> index 29b7fc28c607..2521752c4e4a 100644
> --- a/fs/btrfs/ctree.h
> +++ b/fs/btrfs/ctree.h
> @@ -702,6 +702,11 @@ struct btrfs_delayed_root;
> #define BTRFS_FS_BTREE_ERR 11
> #define BTRFS_FS_LOG1_ERR 12
> #define BTRFS_FS_LOG2_ERR 13
> +/*
> + * Indicate that a whole-filesystem exclusive operation is running
> + * (device replace, resize, device add/delete, balance)
> + */
> +#define BTRFS_FS_EXCL_OP 14
>
> struct btrfs_fs_info {
> u8 fsid[BTRFS_FSID_SIZE];
> @@ -1067,8 +1072,6 @@ struct btrfs_fs_info {
> /* device replace state */
> struct btrfs_dev_replace dev_replace;
>
> - atomic_t mutually_exclusive_operation_running;
> -
> struct percpu_counter bio_counter;
> wait_queue_head_t replace_wait;
>
> diff --git a/fs/btrfs/dev-replace.c b/fs/btrfs/dev-replace.c
> index e653921f05d9..de7b2c897fe0 100644
> --- a/fs/btrfs/dev-replace.c
> +++ b/fs/btrfs/dev-replace.c
> @@ -784,8 +784,7 @@ int btrfs_resume_dev_replace_async(struct btrfs_fs_info *fs_info)
> }
> btrfs_dev_replace_unlock(dev_replace, 1);
>
> - WARN_ON(atomic_xchg(
> - &fs_info->mutually_exclusive_operation_running, 1));
> + WARN_ON(test_and_set_bit(BTRFS_FS_EXCL_OP, &fs_info->flags));
> task = kthread_run(btrfs_dev_replace_kthread, fs_info, "btrfs-devrepl");
> return PTR_ERR_OR_ZERO(task);
> }
> @@ -814,7 +813,7 @@ static int btrfs_dev_replace_kthread(void *data)
> (unsigned int)progress);
> }
> btrfs_dev_replace_continue_on_mount(fs_info);
> - atomic_set(&fs_info->mutually_exclusive_operation_running, 0);
> + clear_bit(BTRFS_FS_EXCL_OP, &fs_info->flags);
>
> return 0;
> }
> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> index dabfc7ac48a6..a29dc3fd7152 100644
> --- a/fs/btrfs/ioctl.c
> +++ b/fs/btrfs/ioctl.c
> @@ -1504,7 +1504,7 @@ static noinline int btrfs_ioctl_resize(struct file *file,
> if (ret)
> return ret;
>
> - if (atomic_xchg(&fs_info->mutually_exclusive_operation_running, 1)) {
> + if (test_and_set_bit(BTRFS_FS_EXCL_OP, &fs_info->flags)) {
> mnt_drop_write_file(file);
> return BTRFS_ERROR_DEV_EXCL_RUN_IN_PROGRESS;
> }
> @@ -1619,7 +1619,7 @@ static noinline int btrfs_ioctl_resize(struct file *file,
> kfree(vol_args);
> out:
> mutex_unlock(&fs_info->volume_mutex);
> - atomic_set(&fs_info->mutually_exclusive_operation_running, 0);
> + clear_bit(BTRFS_FS_EXCL_OP, &fs_info->flags);
> mnt_drop_write_file(file);
> return ret;
> }
> @@ -2661,7 +2661,7 @@ static long btrfs_ioctl_add_dev(struct btrfs_fs_info *fs_info, void __user *arg)
> if (!capable(CAP_SYS_ADMIN))
> return -EPERM;
>
> - if (atomic_xchg(&fs_info->mutually_exclusive_operation_running, 1))
> + if (test_and_set_bit(BTRFS_FS_EXCL_OP, &fs_info->flags))
> return BTRFS_ERROR_DEV_EXCL_RUN_IN_PROGRESS;
>
> mutex_lock(&fs_info->volume_mutex);
> @@ -2680,7 +2680,7 @@ static long btrfs_ioctl_add_dev(struct btrfs_fs_info *fs_info, void __user *arg)
> kfree(vol_args);
> out:
> mutex_unlock(&fs_info->volume_mutex);
> - atomic_set(&fs_info->mutually_exclusive_operation_running, 0);
> + clear_bit(BTRFS_FS_EXCL_OP, &fs_info->flags);
> return ret;
> }
>
> @@ -2708,7 +2708,7 @@ static long btrfs_ioctl_rm_dev_v2(struct file *file, void __user *arg)
> if (vol_args->flags & ~BTRFS_VOL_ARG_V2_FLAGS_SUPPORTED)
> return -EOPNOTSUPP;
>
> - if (atomic_xchg(&fs_info->mutually_exclusive_operation_running, 1)) {
> + if (test_and_set_bit(BTRFS_FS_EXCL_OP, &fs_info->flags)) {
> ret = BTRFS_ERROR_DEV_EXCL_RUN_IN_PROGRESS;
> goto out;
> }
> @@ -2721,7 +2721,7 @@ static long btrfs_ioctl_rm_dev_v2(struct file *file, void __user *arg)
> ret = btrfs_rm_device(fs_info, vol_args->name, 0);
> }
> mutex_unlock(&fs_info->volume_mutex);
> - atomic_set(&fs_info->mutually_exclusive_operation_running, 0);
> + clear_bit(BTRFS_FS_EXCL_OP, &fs_info->flags);
>
> if (!ret) {
> if (vol_args->flags & BTRFS_DEVICE_SPEC_BY_ID)
> @@ -2752,7 +2752,7 @@ static long btrfs_ioctl_rm_dev(struct file *file, void __user *arg)
> if (ret)
> return ret;
>
> - if (atomic_xchg(&fs_info->mutually_exclusive_operation_running, 1)) {
> + if (test_and_set_bit(BTRFS_FS_EXCL_OP, &fs_info->flags)) {
> ret = BTRFS_ERROR_DEV_EXCL_RUN_IN_PROGRESS;
> goto out_drop_write;
> }
> @@ -2772,7 +2772,7 @@ static long btrfs_ioctl_rm_dev(struct file *file, void __user *arg)
> btrfs_info(fs_info, "disk deleted %s", vol_args->name);
> kfree(vol_args);
> out:
> - atomic_set(&fs_info->mutually_exclusive_operation_running, 0);
> + clear_bit(BTRFS_FS_EXCL_OP, &fs_info->flags);
> out_drop_write:
> mnt_drop_write_file(file);
>
> @@ -4442,13 +4442,11 @@ static long btrfs_ioctl_dev_replace(struct btrfs_fs_info *fs_info,
> ret = -EROFS;
> goto out;
> }
> - if (atomic_xchg(
> - &fs_info->mutually_exclusive_operation_running, 1)) {
> + if (test_and_set_bit(BTRFS_FS_EXCL_OP, &fs_info->flags)) {
> ret = BTRFS_ERROR_DEV_EXCL_RUN_IN_PROGRESS;
> } else {
> ret = btrfs_dev_replace_by_ioctl(fs_info, p);
> - atomic_set(
> - &fs_info->mutually_exclusive_operation_running, 0);
> + clear_bit(BTRFS_FS_EXCL_OP, &fs_info->flags);
> }
> break;
> case BTRFS_IOCTL_DEV_REPLACE_CMD_STATUS:
> @@ -4643,7 +4641,7 @@ static long btrfs_ioctl_balance(struct file *file, void __user *arg)
> return ret;
>
> again:
> - if (!atomic_xchg(&fs_info->mutually_exclusive_operation_running, 1)) {
> + if (!test_and_set_bit(BTRFS_FS_EXCL_OP, &fs_info->flags)) {
> mutex_lock(&fs_info->volume_mutex);
> mutex_lock(&fs_info->balance_mutex);
> need_unlock = true;
> @@ -4689,7 +4687,7 @@ static long btrfs_ioctl_balance(struct file *file, void __user *arg)
> }
>
> locked:
> - BUG_ON(!atomic_read(&fs_info->mutually_exclusive_operation_running));
> + BUG_ON(!test_bit(BTRFS_FS_EXCL_OP, &fs_info->flags));
>
> if (arg) {
> bargs = memdup_user(arg, sizeof(*bargs));
> @@ -4745,11 +4743,10 @@ static long btrfs_ioctl_balance(struct file *file, void __user *arg)
>
> do_balance:
> /*
> - * Ownership of bctl and mutually_exclusive_operation_running
> + * Ownership of bctl and filesystem flag BTRFS_FS_EXCL_OP
> * goes to to btrfs_balance. bctl is freed in __cancel_balance,
> * or, if restriper was paused all the way until unmount, in
> - * free_fs_info. mutually_exclusive_operation_running is
> - * cleared in __cancel_balance.
> + * free_fs_info. The flag is cleared in __cancel_balance.
> */
> need_unlock = false;
>
> @@ -4769,7 +4766,7 @@ static long btrfs_ioctl_balance(struct file *file, void __user *arg)
> mutex_unlock(&fs_info->balance_mutex);
> mutex_unlock(&fs_info->volume_mutex);
> if (need_unlock)
> - atomic_set(&fs_info->mutually_exclusive_operation_running, 0);
> + clear_bit(BTRFS_FS_EXCL_OP, &fs_info->flags);
> out:
> mnt_drop_write_file(file);
> return ret;
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index 73d56eef5e60..91580cf471e4 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -3736,7 +3736,7 @@ static void __cancel_balance(struct btrfs_fs_info *fs_info)
> if (ret)
> btrfs_handle_fs_error(fs_info, ret, NULL);
>
> - atomic_set(&fs_info->mutually_exclusive_operation_running, 0);
> + clear_bit(BTRFS_FS_EXCL_OP, &fs_info->flags);
> }
>
> /* Non-zero return value signifies invalidity */
> @@ -3910,7 +3910,7 @@ int btrfs_balance(struct btrfs_balance_control *bctl,
> __cancel_balance(fs_info);
> else {
> kfree(bctl);
> - atomic_set(&fs_info->mutually_exclusive_operation_running, 0);
> + clear_bit(BTRFS_FS_EXCL_OP, &fs_info->flags);
> }
> return ret;
> }
> @@ -4000,7 +4000,7 @@ int btrfs_recover_balance(struct btrfs_fs_info *fs_info)
> btrfs_balance_sys(leaf, item, &disk_bargs);
> btrfs_disk_balance_args_to_cpu(&bctl->sys, &disk_bargs);
>
> - WARN_ON(atomic_xchg(&fs_info->mutually_exclusive_operation_running, 1));
> + WARN_ON(test_and_set_bit(BTRFS_FS_EXCL_OP, &fs_info->flags));
>
> mutex_lock(&fs_info->volume_mutex);
> mutex_lock(&fs_info->balance_mutex);
>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] btrfs: track exclusive filesystem operation in flags
2017-03-29 10:01 ` Anand Jain
@ 2017-03-29 13:21 ` David Sterba
0 siblings, 0 replies; 3+ messages in thread
From: David Sterba @ 2017-03-29 13:21 UTC (permalink / raw)
To: Anand Jain; +Cc: linux-btrfs
On Wed, Mar 29, 2017 at 06:01:37PM +0800, Anand Jain wrote:
>
>
> On 03/28/2017 08:44 PM, David Sterba wrote:
> > There are several operations, usually started from ioctls, that cannot
> > run concurrently. The status is tracked in
> > mutually_exclusive_operation_running as an atomic_t. We can easily track
> > the status as one of the per-filesystem flag bits with same
> > synchronization guarantees.
> >
> > The conversion replaces:
> >
> > * atomic_xchg(..., 1) -> test_and_set_bit(FLAG, ...)
> > * atomic_set(..., 0) -> clear_bit(FLAG, ...)
>
>
> Makes sense.
>
> Reviewed-by: Anand Jain <anand.jain@oracle.com>
>
> However in the long term do you think its better to have
> BTRFS_FS_EXCL_OP flag in the struct btrfs_fs_devices
> rather than in struct btrfs_fs_info ? because we don't have
> fs_info until device is mounted and in the long term we could
> have a feature where volume can be maintained just after the
> device scan without device being mounted.
I can't think of an example where it would be useful to move it out of
fs_info, so I'd need to know more details about the usecase. But the
flag makes sense only after the filesystem is mounted and all devices
are known, so what you suggest would be probably tracked by other flag
if necessary.
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2017-03-29 13:22 UTC | newest]
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2017-03-28 12:44 [PATCH] btrfs: track exclusive filesystem operation in flags David Sterba
2017-03-29 10:01 ` Anand Jain
2017-03-29 13:21 ` David Sterba
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