Re: [PATCH] Btrfs: disallow 'btrfs {balance,replace} cancel' on ro mounts
On Fri, 11 Oct 2013 09:13:24 +0800, Wang Shilong wrote:
On 10/11/2013 01:40 AM, Ilya Dryomov wrote:
I have a question in my mind.
Can we reach a state that there is operation in progress when filesystem
has been readonly?If we do cancel operations on a ro filesystem, we should
get No operations in progress .
Well, it's arguable what ro means. No write to the devices at all? Or
replay log on mount (which means to write to the filesystem), but no
write access in addition to that? Or allow filesystem internal things to
be modified and written to disk, like it was done when the balance or
replace control items were modified on disk when the cancelling was
requested?
In any case, don't make it more complicated then necessary IMO, and
return EROFS if someone calls cancel on a ro filesystem regardless of
the state of the operation. It only adds errors to try to distuingish
such things and is of no benefit for anybody IMHO.
For both balance and replace, cancelling involves changing the on-disk
state and committing a transaction, which is not a good thing to do on
read-only filesystems.
Cc: Stefan Behrens sbehr...@giantdisaster.de
Signed-off-by: Ilya Dryomov idryo...@gmail.com
---
fs/btrfs/dev-replace.c |3 +++
fs/btrfs/volumes.c |3 +++
2 files changed, 6 insertions(+)
diff --git a/fs/btrfs/dev-replace.c b/fs/btrfs/dev-replace.c
index 9efb94e..98df261 100644
--- a/fs/btrfs/dev-replace.c
+++ b/fs/btrfs/dev-replace.c
@@ -650,6 +650,9 @@ static u64 __btrfs_dev_replace_cancel(struct
btrfs_fs_info *fs_info)
u64 result;
int ret;
+if (fs_info-sb-s_flags MS_RDONLY)
+return -EROFS;
+
mutex_lock(dev_replace-lock_finishing_cancel_unmount);
btrfs_dev_replace_lock(dev_replace);
switch (dev_replace-replace_state) {
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index a306db9..2630f38 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -3424,6 +3424,9 @@ int btrfs_pause_balance(struct btrfs_fs_info
*fs_info)
int btrfs_cancel_balance(struct btrfs_fs_info *fs_info)
{
+if (fs_info-sb-s_flags MS_RDONLY)
+return -EROFS;
+
mutex_lock(fs_info-balance_mutex);
if (!fs_info-balance_ctl) {
mutex_unlock(fs_info-balance_mutex);
--
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Re: [PATCH] Btrfs: disallow 'btrfs {balance,replace} cancel' on ro mounts
Op 11-10-2013 11:23, Stefan Behrens schreef:
On Fri, 11 Oct 2013 09:13:24 +0800, Wang Shilong wrote:
On 10/11/2013 01:40 AM, Ilya Dryomov wrote:
I have a question in my mind.
Can we reach a state that there is operation in progress when filesystem
has been readonly?If we do cancel operations on a ro filesystem, we should
get No operations in progress .
Well, it's arguable what ro means. No write to the devices at all? Or
replay log on mount (which means to write to the filesystem), but no
write access in addition to that? Or allow filesystem internal things to
be modified and written to disk, like it was done when the balance or
replace control items were modified on disk when the cancelling was
requested?
In any case, don't make it more complicated then necessary IMO, and
return EROFS if someone calls cancel on a ro filesystem regardless of
the state of the operation. It only adds errors to try to distuingish
such things and is of no benefit for anybody IMHO.
just my 2 cents:
I once had to recover a ext3 filesystem from a device that would crash
if you write anything beyond 2T. The problem is that there was an entry
in the journal telling the OS to do just that. so the device would just
crash every time out mount the filesystem. even in RO mode.
The manual speaks about a 'skip journal replay' option, but it was never
implemented.
kernel source was something like:
case: SKIP_JOURNAL_REPLAY:
return error;
The result: there was no way to mount the filesystem, even in RO mode. i
endedup dd'ing the whole thing to another device, and then mounting the
resulting image. it took a very long time!
i would expect a RO mount never to write anything to a filesystem. not
even replay a journal (or a seperate option for that).
Its possible that the device is not writable at all, if its a snapshot
or a RO iscsi device of some kind.
Remco
For both balance and replace, cancelling involves changing the on-disk
state and committing a transaction, which is not a good thing to do on
read-only filesystems.
Cc: Stefan Behrens sbehr...@giantdisaster.de
Signed-off-by: Ilya Dryomov idryo...@gmail.com
---
fs/btrfs/dev-replace.c |3 +++
fs/btrfs/volumes.c |3 +++
2 files changed, 6 insertions(+)
diff --git a/fs/btrfs/dev-replace.c b/fs/btrfs/dev-replace.c
index 9efb94e..98df261 100644
--- a/fs/btrfs/dev-replace.c
+++ b/fs/btrfs/dev-replace.c
@@ -650,6 +650,9 @@ static u64 __btrfs_dev_replace_cancel(struct
btrfs_fs_info *fs_info)
u64 result;
int ret;
+if (fs_info-sb-s_flags MS_RDONLY)
+return -EROFS;
+
mutex_lock(dev_replace-lock_finishing_cancel_unmount);
btrfs_dev_replace_lock(dev_replace);
switch (dev_replace-replace_state) {
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index a306db9..2630f38 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -3424,6 +3424,9 @@ int btrfs_pause_balance(struct btrfs_fs_info
*fs_info)
int btrfs_cancel_balance(struct btrfs_fs_info *fs_info)
{
+if (fs_info-sb-s_flags MS_RDONLY)
+return -EROFS;
+
mutex_lock(fs_info-balance_mutex);
if (!fs_info-balance_ctl) {
mutex_unlock(fs_info-balance_mutex);
--
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Re: [PATCH] Btrfs: disallow 'btrfs {balance,replace} cancel' on ro mounts
On Fri, Oct 11, 2013 at 4:13 AM, Wang Shilong wangsl.f...@cn.fujitsu.com wrote: On 10/11/2013 01:40 AM, Ilya Dryomov wrote: I have a question in my mind. Can we reach a state that there is operation in progress when filesystem has been readonly?If we do cancel operations on a ro filesystem, we should get No operations in progress . So if I understand you correctly you are saying that we should return the Not in progress error code if the filesystem is mounted ro and there is nothing to cancel. I actually did think about it, but decided against it because one can extend this argument to starting commands with something like If I order a start on a read-only fs and that operation has already been started, I should get EINPROGRESS., and that's not what we are currently doing. Thanks, Ilya -- To unsubscribe from this list: send the line unsubscribe linux-btrfs in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] Btrfs: disallow 'btrfs {balance,replace} cancel' on ro mounts
On Fri, Oct 11, 2013 at 12:28 PM, Remco Hosman - Yerf-IT re...@yerf-it.nl wrote: i would expect a RO mount never to write anything to a filesystem. not even replay a journal (or a seperate option for that). Its possible that the device is not writable at all, if its a snapshot or a RO iscsi device of some kind. I agree, and that's exactly the point of this patch. Thanks, Ilya -- To unsubscribe from this list: send the line unsubscribe linux-btrfs in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] Btrfs: disallow 'btrfs {balance,replace} cancel' on ro mounts
On Fri, 11 Oct 2013 11:23:04 +0200 Stefan Behrens sbehr...@giantdisaster.de wrote: On Fri, 11 Oct 2013 09:13:24 +0800, Wang Shilong wrote: On 10/11/2013 01:40 AM, Ilya Dryomov wrote: I have a question in my mind. Can we reach a state that there is operation in progress when filesystem has been readonly?If we do cancel operations on a ro filesystem, we should get No operations in progress . Well, it's arguable what ro means. No write to the devices at all? If I had an FS image and mounted it as -o loop,ro I'd simply expect md5sum of that image to match before mount and after unmount, i.e. no writes at all. Really, how can one argue with what read only means? If it will mean something else than a complete absence of writes, then how can we mount devices or FS images to do forensics, etc? Or do a recovery from a difficult corruption or try to debug an FS crash. -- With respect, Roman signature.asc Description: PGP signature
Re: [PATCH] Btrfs: disallow 'btrfs {balance,replace} cancel' on ro mounts
On Fri, Oct 11, 2013 at 03:35:46PM +0600, Roman Mamedov wrote: On Fri, 11 Oct 2013 11:23:04 +0200 Stefan Behrens sbehr...@giantdisaster.de wrote: On Fri, 11 Oct 2013 09:13:24 +0800, Wang Shilong wrote: On 10/11/2013 01:40 AM, Ilya Dryomov wrote: I have a question in my mind. Can we reach a state that there is operation in progress when filesystem has been readonly?If we do cancel operations on a ro filesystem, we should get No operations in progress . Well, it's arguable what ro means. No write to the devices at all? If I had an FS image and mounted it as -o loop,ro I'd simply expect md5sum of that image to match before mount and after unmount, i.e. no writes at all. Really, how can one argue with what read only means? If it will mean something else than a complete absence of writes, then how can we mount devices or FS images to do forensics, etc? Or do a recovery from a difficult corruption or try to debug an FS crash. I think the issue here is that with ext3,4 the FS data structures can be in an inconsistent (i.e. broken) state unless you do the journal replay, so you're left with the choice of replay the journal and have a working filesystem that you can't write to, or don't modify anything, and have a useless filesystem with errors you could fix with the information in the journal. Fortunately, we don't (well, shouldn't) have that issue in btrfs -- if we don't replay the log, we've still got a consistent FS, so it's much easier conceptually to mount an FS read-only (with the proviso that a RO mount may be missing some data that was saved earlier, but you'll get that back if you allow the log reply with a rw mount later). Hugo. -- === Hugo Mills: hugo@... carfax.org.uk | darksatanic.net | lug.org.uk === PGP key: 65E74AC0 from wwwkeys.eu.pgp.net or http://www.carfax.org.uk --- Gentlemen! You can't fight here! This is the War Room! --- signature.asc Description: Digital signature
[PATCH] Btrfs: disallow 'btrfs {balance,replace} cancel' on ro mounts
For both balance and replace, cancelling involves changing the on-disk
state and committing a transaction, which is not a good thing to do on
read-only filesystems.
Cc: Stefan Behrens sbehr...@giantdisaster.de
Signed-off-by: Ilya Dryomov idryo...@gmail.com
---
fs/btrfs/dev-replace.c |3 +++
fs/btrfs/volumes.c |3 +++
2 files changed, 6 insertions(+)
diff --git a/fs/btrfs/dev-replace.c b/fs/btrfs/dev-replace.c
index 9efb94e..98df261 100644
--- a/fs/btrfs/dev-replace.c
+++ b/fs/btrfs/dev-replace.c
@@ -650,6 +650,9 @@ static u64 __btrfs_dev_replace_cancel(struct btrfs_fs_info
*fs_info)
u64 result;
int ret;
+ if (fs_info-sb-s_flags MS_RDONLY)
+ return -EROFS;
+
mutex_lock(dev_replace-lock_finishing_cancel_unmount);
btrfs_dev_replace_lock(dev_replace);
switch (dev_replace-replace_state) {
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index a306db9..2630f38 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -3424,6 +3424,9 @@ int btrfs_pause_balance(struct btrfs_fs_info *fs_info)
int btrfs_cancel_balance(struct btrfs_fs_info *fs_info)
{
+ if (fs_info-sb-s_flags MS_RDONLY)
+ return -EROFS;
+
mutex_lock(fs_info-balance_mutex);
if (!fs_info-balance_ctl) {
mutex_unlock(fs_info-balance_mutex);
--
1.7.10.4
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Re: [PATCH] Btrfs: disallow 'btrfs {balance,replace} cancel' on ro mounts
On 10/11/2013 01:40 AM, Ilya Dryomov wrote:
I have a question in my mind.
Can we reach a state that there is operation in progress when filesystem
has been readonly?If we do cancel operations on a ro filesystem, we should
get No operations in progress .
Thanks,
Wang
For both balance and replace, cancelling involves changing the on-disk
state and committing a transaction, which is not a good thing to do on
read-only filesystems.
Cc: Stefan Behrens sbehr...@giantdisaster.de
Signed-off-by: Ilya Dryomov idryo...@gmail.com
---
fs/btrfs/dev-replace.c |3 +++
fs/btrfs/volumes.c |3 +++
2 files changed, 6 insertions(+)
diff --git a/fs/btrfs/dev-replace.c b/fs/btrfs/dev-replace.c
index 9efb94e..98df261 100644
--- a/fs/btrfs/dev-replace.c
+++ b/fs/btrfs/dev-replace.c
@@ -650,6 +650,9 @@ static u64 __btrfs_dev_replace_cancel(struct btrfs_fs_info
*fs_info)
u64 result;
int ret;
+ if (fs_info-sb-s_flags MS_RDONLY)
+ return -EROFS;
+
mutex_lock(dev_replace-lock_finishing_cancel_unmount);
btrfs_dev_replace_lock(dev_replace);
switch (dev_replace-replace_state) {
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index a306db9..2630f38 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -3424,6 +3424,9 @@ int btrfs_pause_balance(struct btrfs_fs_info *fs_info)
int btrfs_cancel_balance(struct btrfs_fs_info *fs_info)
{
+ if (fs_info-sb-s_flags MS_RDONLY)
+ return -EROFS;
+
mutex_lock(fs_info-balance_mutex);
if (!fs_info-balance_ctl) {
mutex_unlock(fs_info-balance_mutex);
--
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