Below shows the bug cascading to this patch.
And now to fix this I think we shouldn't fix/workaround in the
btrfs-progs again!, fix it in the btrfs-kernel (or leave it open
until suitable fix is found, I tried and failed. but don't fix it
in a wrong way). If you want to help to fix this problem: Find out
if we could get kobject notification with in kernel when disks gets
disappeared.
I have been advocating btrfs-progs should _not_ add its intelligence
and it should be as transparent as possible in showing the kernel's
status. This should be seriously considered.
(-----------
For patches to take this approach the core problem here is different
and hope we could correct it..
First, we have a superficial and wrong measuring tape (xfstest) and
we are trying to fix the product using it And in between is btrfs-progs
which is trying to add more superficial-ness.
2nd, btrfs Wiki has a theory and thus sets the direction that
btrfs-progs would copy code from btrfs-kernel, I seriously doubt
if that's a good idea.
If you want to make btrfs-progs as intelligent as btrfs-kernel
(which I don't understand why you should ? since the purpose of
btrfs-progs and btrfs-kernel are different) then first you need
develop a mini synchronization mechanism between btrfs-progs and btrfs
kernel which is as good as two active nodes FS which says from my
experience with Solaris/SAM-QFS. Developing a synchronization
mechanism is not in the plan here. Further from the End user
Application (DB) performance perspective calling sync at the need of
something like btrfs-progs is a very very bad idea. Applications would
experience jitters in their steady state performance. Once Solaris had
this issue and we fixed it.
-----------)
Have fun. ;-)
----------------------------------------------------------------
$ btrfs dev scan
Scanning for Btrfs filesystems
$ mount /dev/sdc /btrfs
$ btrfs fi show
Label: none uuid: dfbf136d-e8d2-489b-8ee1-be0d5999769d
Total devices 2 FS bytes used 663.81MiB
devid 1 size 1.10GiB used 1.10GiB path /dev/sdf
devid 2 size 1.10GiB used 1.08GiB path /dev/sdc
$ devmgt show
host0 sda
host1 sdf
host2 sdc
host3 sdd
host4 sde
$ devmgt detach /dev/sdf
-----/dev/kmsg----
sd 1:0:0:0: [sdf] Stopping disk
SUBSYSTEM=scsi
DEVICE=+scsi:1:0:0:0
ata2.00: disabled
------------------
detach /dev/sdf successful
(as a known bug btrfs kernel does not know device is missing, missing
flag isn't set, as shown below)
$ btrfs-devlist
fsid name uuid (seed_fsid sprout_fsid)
(fs_latest_devid fs_num_devices fs_open_devices fs_rw_devices
fs_missing_devices fs_total_devices) fs_total_rw_bytes
fs_num_can_discard fs_latest_trans
devid gen total_bytes disk_total_bytes bytes_used type io_align
io_width sector_size fmode
fs_flags
dev_flags
dfbf136d-e8d2-489b-8ee1-be0d5999769d /dev/sdf
13715cc5-3aeb-4523-b02c-a072fd427a00 (null null)
(2 2 2 2 0 2) 2363490304 0 7
1 5 1181745152 1181745152 1181745152 0 4096 4096 4096 0x83
fs_Mounted|not_fs_Seeding|fs_Rotating
Writable|MD|not_Missing|not_Discard|not_Replace_tgt|not_Run_pending|not_Nobarriers|Stat_valid|Stat_dirty|Bdev
dfbf136d-e8d2-489b-8ee1-be0d5999769d /dev/sdc
12ad34f7-8d58-44fa-95cf-b2bbc0cec69d (null null)
(2 2 2 2 0 2) 2363490304 0 7
2 7 1181745152 1181745152 1160773632 0 4096 4096 4096 0x83
fs_Mounted|not_fs_Seeding|fs_Rotating
Writable|MD|not_Missing|not_Discard|not_Replace_tgt|not_Run_pending|not_Nobarriers|Stat_valid|Stat_dirty|Bdev
(below btrfs-progs patch added intelligence to tell the world that
device is missing)
Ref:
~~~~~~~
commit 2ae6a037efd52ae0fa30052d456ad07f074f5d54
Author: Qu Wenruo <quwenruo@xxxxxxxxxxxxxx>
Date: Fri Feb 7 15:07:19 2014 +0800
btrfs-progs: Add missing devices check for mounted btrfs.
~~~~~~~
$ btrfs fi show
Label: none uuid: dfbf136d-e8d2-489b-8ee1-be0d5999769d
Total devices 2 FS bytes used 663.81MiB
devid 2 size 1.10GiB used 1.08GiB path /dev/sdc
*** Some devices missing
$ btrfs dev add /dev/sde /btrfs
$ btrfs fi show
Label: none uuid: dfbf136d-e8d2-489b-8ee1-be0d5999769d
Total devices 3 FS bytes used 663.81MiB
devid 2 size 1.10GiB used 1.08GiB path /dev/sdc
devid 3 size 1.04GiB used 0.00 path /dev/sde
*** Some devices missing
Now the bug is delete missing fails. Since kernel don't
understand whats missing.
$ btrfs dev del missing /btrfs
ERROR: error removing the device 'missing' - no missing devices found to
remove
$
---------------------------------------------------------------------------
On 02/10/2014 08:36 AM, Qu Wenruo wrote:
On Fri, 07 Feb 2014 17:34:46 +0800, Anand Jain wrote:
IMO btrfs-progs shouldn't add its intelligence to know if disk
is missing. If btrfs-kernel doesn't know when disk is missing
that's a bug to fix in btrfs-kernel. yes that indeed true as
of now in btrfs-kernel. btrfs kernel has no idea when disk
goes missing, just -EIO doesn't tell btrfs that. I am trying
to fix this first.
But the problem is there isn't good way with in btrfs/FS
to know when disk goes missing. did I miss anything ?
Yes, kernel detection is the best way.
But since it has no better way to detect missing device, I think the
btrfs-progs way fix is good enough for now.
Since btrfs fi show with "-d" options will scan the /dev to find fs and
check missing disks,
I think adds some user-land check even using the ioctl way is still
somewhat reasonable.
Thanks
Qu
Thanks, Anand
On 02/07/2014 02:45 PM, Qu Wenruo wrote:
In btrfs/003 of xfstest, it will check whether btrfs fi show can find
missing devices.
But before the patch, btrfs-progs will not check whether device missing
if given a mounted btrfs mountpoint/block device.
This patch fixes the bug and will pass btrfs/003.
Signed-off-by: Qu Wenruo <quwenruo@xxxxxxxxxxxxxx>
Cc: Anand Jain <anand.jain@xxxxxxxxxx>
---
cmds-filesystem.c | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff --git a/cmds-filesystem.c b/cmds-filesystem.c
index 384d1b9..4c9933d 100644
--- a/cmds-filesystem.c
+++ b/cmds-filesystem.c
@@ -363,6 +363,8 @@ static int print_one_fs(struct
btrfs_ioctl_fs_info_args *fs_info,
char *label, char *path)
{
int i;
+ int fd;
+ int missing;
char uuidbuf[BTRFS_UUID_UNPARSED_SIZE];
struct btrfs_ioctl_dev_info_args *tmp_dev_info;
int ret;
@@ -385,6 +387,14 @@ static int print_one_fs(struct
btrfs_ioctl_fs_info_args *fs_info,
for (i = 0; i < fs_info->num_devices; i++) {
tmp_dev_info = (struct btrfs_ioctl_dev_info_args
*)&dev_info[i];
+
+ /* Add check for missing devices even mounted */
+ fd = open((char *)tmp_dev_info->path, O_RDONLY);
+ if (fd < 0) {
+ missing = 1;
+ continue;
+ }
+ close(fd);
printf("\tdevid %4llu size %s used %s path %s\n",
tmp_dev_info->devid,
pretty_size(tmp_dev_info->total_bytes),
@@ -392,6 +402,8 @@ static int print_one_fs(struct
btrfs_ioctl_fs_info_args *fs_info,
tmp_dev_info->path);
}
+ if (missing)
+ printf("\t*** Some devices missing\n");
printf("\n");
return 0;
}
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