Discussion:
[PATCH] btrfs: ioctl BTRFS_IOC_FS_INFO and BTRFS_IOC_DEV_INFO miss-matched with slots
(too old to reply)
Anand Jain
2014-08-16 03:08:07 UTC
Permalink
Raw Message
ioctl BTRFS_IOC_FS_INFO return num_devices which does _not_ include seed
device, But the following ioctl BTRFS_IOC_DEV_INFO counts and gets seed
disk when probed. So in the userland we hit a count-slot missmatch
bug..
get_fs_info()
::
BUG_ON(ndevs >= fi_args->num_devices);
which hits this bug when we have mounted a seed device.

So to fix this problem here in this patch ioctl BTRFS_IOC_FS_INFO
will provide total_devices instead of num_devices.

This would fix the problem partly. Partly because ealier num_devices
included the replacing device but now total_device does not include
the replacing device. Getting a count which includes a transient device
is rather too in efficient/wrong indeed, because there can be a race
condition where in the time between ioctl BTRFS_IOC_FS_INFO to
BTRFS_IOC_DEV_INFO the replace device operation might have been
completed. So to fix this problem its better that user land btrfs-progs
probes replacing device (at devid 0) separately.

v2:
Agree with Wang's comment. Its better to show seed disks under the
sprout fs, so that user can establish mapping of seed to sprout devices.

So here I am making BTRFS_IOC_FS_INFO to return the total_devices
which would count the seed devices (but not the replacing device).
A btrfs-progs patch will separately probe for devid 0 (which is
a replacing transient device when present).

v1:
This patch will make BTRFS_IOC_DEV_INFO ioctl to provide disks only
of the FSID being probed (seed disks are under different FSID).

which means when seed is still not deleted from the sprout the btrfs
filesystem show command will show disks them under their
respective FSIDs

Signed-off-by: Anand Jain <***@oracle.com>
---
fs/btrfs/ioctl.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index da73ab3..05dd88b 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -2725,7 +2725,7 @@ static long btrfs_ioctl_fs_info(struct btrfs_root *root, void __user *arg)
return -ENOMEM;

mutex_lock(&fs_devices->device_list_mutex);
- fi_args->num_devices = fs_devices->num_devices;
+ fi_args->num_devices = fs_devices->total_devices;
memcpy(&fi_args->fsid, root->fs_info->fsid, sizeof(fi_args->fsid));

list_for_each_entry_safe(device, next, &fs_devices->devices, dev_list) {
--
2.0.0.153.g79dcccc

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Anand Jain
2014-08-16 03:08:08 UTC
Permalink
Raw Message
The count as returned by BTRFS_IOC_FS_INFO is the number of slots that
btrfs-progs would allocate for the BTRFS_IOC_DEV_INFO ioctl. Since
BTRFS_IOC_DEV_INFO would loop across the seed devices, So its better
ioctl BTRFS_IOC_FS_INFO returns the total_devices instead of num_devices.

The above mentioned patch just does that. That is, it returns
total_devices instead of num_devices.

Which means we need to probe for the replacing device separately.

This patch will probe for the replacing device separately.

Signed-off-by: Anand Jain <***@oracle.com>
---
utils.c | 19 ++++++++++++++++++-
1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/utils.c b/utils.c
index 8bdc2a7..fa837b9 100644
--- a/utils.c
+++ b/utils.c
@@ -1929,12 +1929,29 @@ int get_fs_info(char *path, struct btrfs_ioctl_fs_info_args *fi_args,
if (!fi_args->num_devices)
goto out;

- di_args = *di_ret = malloc(fi_args->num_devices * sizeof(*di_args));
+ /*
+ * with kernel patch
+ * btrfs: ioctl BTRFS_IOC_FS_INFO and BTRFS_IOC_DEV_INFO miss-matched with slots
+ * the kernel now returns total_devices which does not include
+ * replacing device if running.
+ * As we need to get dev info of the replace device if it is running,
+ * so just add one to fi_args->num_devices.
+ */
+
+ di_args = *di_ret = malloc((fi_args->num_devices + 1) * sizeof(*di_args));
if (!di_args) {
ret = -errno;
goto out;
}

+ /* get the replace target device if it is there */
+ ret = get_device_info(fd, i, &di_args[ndevs]);
+ if (!ret) {
+ ndevs++;
+ fi_args->num_devices++;
+ }
+ i++;
+
for (; i <= fi_args->max_id; ++i) {
BUG_ON(ndevs >= fi_args->num_devices);
ret = get_device_info(fd, i, &di_args[ndevs]);
--
2.0.0.153.g79dcccc

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Anand Jain
2014-08-18 08:38:18 UTC
Permalink
Raw Message
ioctl BTRFS_IOC_FS_INFO return num_devices which does _not_ include seed
device, But the following ioctl BTRFS_IOC_DEV_INFO counts and gets seed
disk when probed. So in the userland we hit a count-slot missmatch
bug..
get_fs_info()
::
BUG_ON(ndevs >= fi_args->num_devices);
which hits this bug when we have mounted a seed device.

So to fix this problem here in this patch ioctl BTRFS_IOC_FS_INFO
will provide total_devices instead of num_devices.

This would fix the problem partly. Partly because ealier num_devices
included the replacing device but now total_device does not include
the replacing device. Getting a count which includes a transient device
is rather too in efficient/wrong indeed, because there can be a race
condition where in the time between ioctl BTRFS_IOC_FS_INFO to
BTRFS_IOC_DEV_INFO the replace device operation might have been
completed. So to fix this problem its better that user land btrfs-progs
probes replacing device (at devid 0) separately.

v2:
Agree with Wang's comment. Its better to show seed disks under the
sprout fs, so that user can establish mapping of seed to sprout devices.

So here I am making BTRFS_IOC_FS_INFO to return the total_devices
which would count the seed devices (but not the replacing device).
A btrfs-progs patch will separately probe for devid 0 (which is
a replacing transient device when present).

v1:
This patch will make BTRFS_IOC_DEV_INFO ioctl to provide disks only
of the FSID being probed (seed disks are under different FSID).

which means when seed is still not deleted from the sprout the btrfs
filesystem show command will show disks them under their
respective FSIDs

Signed-off-by: Anand Jain <***@oracle.com>
---
v2: a new kind of fix. which would allow seed to be shown in
the btrfs fi show cli output.

fs/btrfs/ioctl.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index da73ab3..05dd88b 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -2725,7 +2725,7 @@ static long btrfs_ioctl_fs_info(struct btrfs_root *root, void __user *arg)
return -ENOMEM;

mutex_lock(&fs_devices->device_list_mutex);
- fi_args->num_devices = fs_devices->num_devices;
+ fi_args->num_devices = fs_devices->total_devices;
memcpy(&fi_args->fsid, root->fs_info->fsid, sizeof(fi_args->fsid));

list_for_each_entry_safe(device, next, &fs_devices->devices, dev_list) {
--
2.0.0.153.g79dcccc

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Anand Jain
2014-09-04 12:02:21 UTC
Permalink
Raw Message
Post by Anand Jain
ioctl BTRFS_IOC_FS_INFO return num_devices which does _not_ include seed
device, But the following ioctl BTRFS_IOC_DEV_INFO counts and gets seed
disk when probed. So in the userland we hit a count-slot missmatch
bug..
get_fs_info()
BUG_ON(ndevs >= fi_args->num_devices);
which hits this bug when we have mounted a seed device.
So to fix this problem here in this patch ioctl BTRFS_IOC_FS_INFO
will provide total_devices instead of num_devices.
The ioctl is very unclear what the 'num_device' actually means.
Right. Thats also true in kernel. very messy. very confusing.
tool btrfs-devlist would help understand whats going on.

----
$ egrep num_device *.c | egrep "total_device"
ioctl.c: fi_args->num_devices = fs_devices->total_devices;
super.c: ret = !(fs_devices->num_devices == fs_devices->total_devices);
volumes.c: total_devices = btrfs_super_num_devices(disk_super);
----

By the way about BTRFS_IOC_DEVICES_READY ioctl above its long time
broken with seed/replace, just waiting to get these patches integrated
first so to fix it later.
Post by Anand Jain
This would fix the problem partly. Partly because ealier num_devices
included the replacing device but now total_device does not include
the replacing device. Getting a count which includes a transient device
is rather too in efficient/wrong indeed, because there can be a race
condition where in the time between ioctl BTRFS_IOC_FS_INFO to
BTRFS_IOC_DEV_INFO the replace device operation might have been
completed. So to fix this problem its better that user land btrfs-progs
probes replacing device (at devid 0) separately.
Agree with Wang's comment. Its better to show seed disks under the
sprout fs, so that user can establish mapping of seed to sprout devices.
So here I am making BTRFS_IOC_FS_INFO to return the total_devices
which would count the seed devices (but not the replacing device).
This is even more confusing. I think we need to add another member to
the ioctl struct to reflect the number of regular devices (num_devices)
and the true total number of devices including seeding and replaced
devices.
that will be a better way. thanks.
The difference should be accompanied by a flag that would say
if there's a seeding or replace in progress.
There are some backward compatibility concerns. Setting num_devices to
total_devices changes semantics of the ioctl, so I think it should stay
as is for now,
As I have tested there is not backward compatibility issue.
But from semantics perspective .. agreed.
but the BUG_ON can be removed and replaced by code that
reallocates the buffer or allocates a few more items in advance.
We don't know how may seed devices are there for a sprout FS.
So thats not possible.

Will review resubmit.

Thanks for commenting.

Anand
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Gui Hecheng
2014-10-17 01:58:17 UTC
Permalink
Raw Message
Post by Anand Jain
Post by Anand Jain
ioctl BTRFS_IOC_FS_INFO return num_devices which does _not_ include seed
device, But the following ioctl BTRFS_IOC_DEV_INFO counts and gets seed
disk when probed. So in the userland we hit a count-slot missmatch
bug..
get_fs_info()
BUG_ON(ndevs >= fi_args->num_devices);
which hits this bug when we have mounted a seed device.
So to fix this problem here in this patch ioctl BTRFS_IOC_FS_INFO
will provide total_devices instead of num_devices.
The ioctl is very unclear what the 'num_device' actually means.
Right. Thats also true in kernel. very messy. very confusing.
tool btrfs-devlist would help understand whats going on.
----
$ egrep num_device *.c | egrep "total_device"
ioctl.c: fi_args->num_devices = fs_devices->total_devices;
super.c: ret = !(fs_devices->num_devices == fs_devices->total_devices);
volumes.c: total_devices = btrfs_super_num_devices(disk_super);
----
By the way about BTRFS_IOC_DEVICES_READY ioctl above its long time
broken with seed/replace, just waiting to get these patches integrated
first so to fix it later.
Post by Anand Jain
This would fix the problem partly. Partly because ealier num_devices
included the replacing device but now total_device does not include
the replacing device. Getting a count which includes a transient device
is rather too in efficient/wrong indeed, because there can be a race
condition where in the time between ioctl BTRFS_IOC_FS_INFO to
BTRFS_IOC_DEV_INFO the replace device operation might have been
completed. So to fix this problem its better that user land btrfs-progs
probes replacing device (at devid 0) separately.
Agree with Wang's comment. Its better to show seed disks under the
sprout fs, so that user can establish mapping of seed to sprout devices.
So here I am making BTRFS_IOC_FS_INFO to return the total_devices
which would count the seed devices (but not the replacing device).
This is even more confusing. I think we need to add another member to
the ioctl struct to reflect the number of regular devices (num_devices)
and the true total number of devices including seeding and replaced
devices.
that will be a better way. thanks.
The difference should be accompanied by a flag that would say
if there's a seeding or replace in progress.
There are some backward compatibility concerns. Setting num_devices to
total_devices changes semantics of the ioctl, so I think it should stay
as is for now,
As I have tested there is not backward compatibility issue.
But from semantics perspective .. agreed.
but the BUG_ON can be removed and replaced by code that
reallocates the buffer or allocates a few more items in advance.
We don't know how may seed devices are there for a sprout FS.
So thats not possible.
Will review resubmit.
Thanks for commenting.
Hi all,

Firtly, thanks for the fix, Anand, how's the new version going?

I've been testing the btrfs fi show cmd these days and find that
this patch has not been merged into linus's tree yet.

Since the suggested way of adding member to the ioctl struct brings
compatibility issues, it may need more discussion.

But since this fix really incluence much to the user, I consider merging
this version first to be a good idea.

What do you think, Chris?

Thanks,
Gui
Post by Anand Jain
Anand
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Anand Jain
2014-10-20 08:17:58 UTC
Permalink
Raw Message
inline as below.
Post by Gui Hecheng
Post by Anand Jain
Post by Anand Jain
ioctl BTRFS_IOC_FS_INFO return num_devices which does _not_ include seed
device, But the following ioctl BTRFS_IOC_DEV_INFO counts and gets seed
disk when probed. So in the userland we hit a count-slot missmatch
bug..
get_fs_info()
BUG_ON(ndevs >= fi_args->num_devices);
which hits this bug when we have mounted a seed device.
So to fix this problem here in this patch ioctl BTRFS_IOC_FS_INFO
will provide total_devices instead of num_devices.
The ioctl is very unclear what the 'num_device' actually means.
Right. Thats also true in kernel. very messy. very confusing.
tool btrfs-devlist would help understand whats going on.
----
$ egrep num_device *.c | egrep "total_device"
ioctl.c: fi_args->num_devices = fs_devices->total_devices;
super.c: ret = !(fs_devices->num_devices == fs_devices->total_devices);
volumes.c: total_devices = btrfs_super_num_devices(disk_super);
----
By the way about BTRFS_IOC_DEVICES_READY ioctl above its long time
broken with seed/replace, just waiting to get these patches integrated
first so to fix it later.
Post by Anand Jain
This would fix the problem partly. Partly because ealier num_devices
included the replacing device but now total_device does not include
the replacing device. Getting a count which includes a transient device
is rather too in efficient/wrong indeed, because there can be a race
condition where in the time between ioctl BTRFS_IOC_FS_INFO to
BTRFS_IOC_DEV_INFO the replace device operation might have been
completed. So to fix this problem its better that user land btrfs-progs
probes replacing device (at devid 0) separately.
Agree with Wang's comment. Its better to show seed disks under the
sprout fs, so that user can establish mapping of seed to sprout devices.
So here I am making BTRFS_IOC_FS_INFO to return the total_devices
which would count the seed devices (but not the replacing device).
This is even more confusing. I think we need to add another member to
the ioctl struct to reflect the number of regular devices (num_devices)
and the true total number of devices including seeding and replaced
devices.
that will be a better way. thanks.
The difference should be accompanied by a flag that would say
if there's a seeding or replace in progress.
There are some backward compatibility concerns. Setting num_devices to
total_devices changes semantics of the ioctl, so I think it should stay
as is for now,
As I have tested there is not backward compatibility issue.
But from semantics perspective .. agreed.
but the BUG_ON can be removed and replaced by code that
reallocates the buffer or allocates a few more items in advance.
We don't know how may seed devices are there for a sprout FS.
So thats not possible.
Will review resubmit.
Thanks for commenting.
Hi all,
Firtly, thanks for the fix, Anand, how's the new version going?
I've been testing the btrfs fi show cmd these days and find that
this patch has not been merged into linus's tree yet.
Since the suggested way of adding member to the ioctl struct brings
compatibility issues, it may need more discussion.
Thanks Gui for commenting.

Yes discussion is needed. Mainly on our long term plan for a better
btrfs kernel device and parameter read interface. which also means
current bugs can wait for this new interface instead of patching the
old structures and bring in a new compatibility mess.

Thanks, Anand
Post by Gui Hecheng
But since this fix really incluence much to the user, I consider merging
this version first to be a good idea.
What do you think, Chris?
Thanks,
Gui
Post by Anand Jain
Anand
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Anand Jain
2014-08-18 08:38:19 UTC
Permalink
Raw Message
As mentioned in the kernel patch

btrfs: ioctl BTRFS_IOC_FS_INFO and
BTRFS_IOC_DEV_INFO miss-matched with slots

The count as returned by BTRFS_IOC_FS_INFO is the number of slots that
btrfs-progs would allocate for the BTRFS_IOC_DEV_INFO ioctl. Since
BTRFS_IOC_DEV_INFO would loop across the seed devices, So its better
ioctl BTRFS_IOC_FS_INFO returns the total_devices instead of num_devices.

The above mentioned patch just does that. That is, it returns
total_devices instead of num_devices.

Which means we need to probe for the replacing device separately.

This patch will probe for the replacing device separately.

Signed-off-by: Anand Jain <***@oracle.com>
---
v2: commit update

utils.c | 19 ++++++++++++++++++-
1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/utils.c b/utils.c
index 8bdc2a7..fa837b9 100644
--- a/utils.c
+++ b/utils.c
@@ -1929,12 +1929,29 @@ int get_fs_info(char *path, struct btrfs_ioctl_fs_info_args *fi_args,
if (!fi_args->num_devices)
goto out;

- di_args = *di_ret = malloc(fi_args->num_devices * sizeof(*di_args));
+ /*
+ * with kernel patch
+ * btrfs: ioctl BTRFS_IOC_FS_INFO and BTRFS_IOC_DEV_INFO miss-matched with slots
+ * the kernel now returns total_devices which does not include
+ * replacing device if running.
+ * As we need to get dev info of the replace device if it is running,
+ * so just add one to fi_args->num_devices.
+ */
+
+ di_args = *di_ret = malloc((fi_args->num_devices + 1) * sizeof(*di_args));
if (!di_args) {
ret = -errno;
goto out;
}

+ /* get the replace target device if it is there */
+ ret = get_device_info(fd, i, &di_args[ndevs]);
+ if (!ret) {
+ ndevs++;
+ fi_args->num_devices++;
+ }
+ i++;
+
for (; i <= fi_args->max_id; ++i) {
BUG_ON(ndevs >= fi_args->num_devices);
ret = get_device_info(fd, i, &di_args[ndevs]);
--
2.0.0.153.g79dcccc

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Anand Jain
2014-08-18 08:38:17 UTC
Permalink
Raw Message
yeah. btrfs filesystem show didn't work any time before as in
the test case below.

mkfs.btrfs /dev/sdb -f
btrfstune -S 1 /dev/sdb
mount /dev/sdb /btrfs
btrfs dev add /dev/sdc /btrfs
btrfs fi show <-- fails.

kindly ref to the commit log for bug and its fix details.

Anand Jain (1):
btrfs-progs: do a separate probe for _transient_ replacing device
As mentioned in the kernel patch btrfs: ioctl
BTRFS_IOC_FS_INFO and BTRFS_IOC_DEV_INFO miss-matched with slots

utils.c | 19 ++++++++++++++++++-
1 file changed, 18 insertions(+), 1 deletion(-)

Anand Jain (1):
btrfs: ioctl BTRFS_IOC_FS_INFO and BTRFS_IOC_DEV_INFO miss-matched
with slots

fs/btrfs/ioctl.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--
2.0.0.153.g79dcccc

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