* [PATCH] btrfs-progs: change mans to describe the third copy of superblock
@ 2017-10-19 7:45 Satoru Takeuchi
2017-10-19 8:34 ` Misono, Tomohiro
0 siblings, 1 reply; 4+ messages in thread
From: Satoru Takeuchi @ 2017-10-19 7:45 UTC (permalink / raw)
To: linux-btrfs
Some tools can select which superblock these commands use by "-s <superblock>"
option. Although this option says the valid values are 0-2, we can set 3
if filesystem is very large.
Signed-off-by: Satoru Takeuchi <satoru.takeuchi@gmail.com>
---
Documentation/btrfs-check.asciidoc | 2 +-
Documentation/btrfs-restore.asciidoc | 2 +-
Documentation/btrfs-select-super.asciidoc | 3 ++-
3 files changed, 4 insertions(+), 3 deletions(-)
diff --git a/Documentation/btrfs-check.asciidoc b/Documentation/btrfs-check.asciidoc
index fbf4884..a557cff 100644
--- a/Documentation/btrfs-check.asciidoc
+++ b/Documentation/btrfs-check.asciidoc
@@ -74,7 +74,7 @@ run in read-only mode, this option exists to calm potential panic when users
are going to run the checker
-s|--super <superblock>::
-use 'superblock'th superblock copy, valid values are 0, 1 or 2 if the
+use 'superblock'th superblock copy, valid values are 0, 1, 2 or 3 if the
respective superblock offset is within the device size
+
This can be used to use a different starting point if some of the primary
diff --git a/Documentation/btrfs-restore.asciidoc b/Documentation/btrfs-restore.asciidoc
index 090dcc5..c19e0e2 100644
--- a/Documentation/btrfs-restore.asciidoc
+++ b/Documentation/btrfs-restore.asciidoc
@@ -63,7 +63,7 @@ use <bytenr> to read the root tree
only restore files that are under specified subvolume root pointed by <bytenr>
-u|--super <mirror>::
-use given superblock mirror identified by <mirror>, it can be 0,1 or 2
+use given superblock mirror identified by <mirror>, it can be 0, 1, 2 or 3
-r|--root <rootid>::
only restore files that are under a specified subvolume whose objectid is <rootid>
diff --git a/Documentation/btrfs-select-super.asciidoc b/Documentation/btrfs-select-super.asciidoc
index 6e94a03..7f96bd8 100644
--- a/Documentation/btrfs-select-super.asciidoc
+++ b/Documentation/btrfs-select-super.asciidoc
@@ -32,13 +32,14 @@ Superblock copies exist in the following offsets on the device:
- primary: '64KiB' (65536)
- 1st copy: '64MiB' (67108864)
- 2nd copy: '256GiB' (274877906944)
+- 3rd copy: '1PiB' (1125899906842624)
A superblock size is '4KiB' (4096).
OPTIONS
-------
-s|--super <superblock>::
-use 'superblock'th superblock copy, valid values are 0 1 or 2 if the
+use 'superblock'th superblock copy, valid values are 0, 1, 2 or 3 if the
respective superblock offset is within the device size
SEE ALSO
--
2.7.4
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] btrfs-progs: change mans to describe the third copy of superblock
2017-10-19 7:45 [PATCH] btrfs-progs: change mans to describe the third copy of superblock Satoru Takeuchi
@ 2017-10-19 8:34 ` Misono, Tomohiro
2017-10-19 9:05 ` Qu Wenruo
0 siblings, 1 reply; 4+ messages in thread
From: Misono, Tomohiro @ 2017-10-19 8:34 UTC (permalink / raw)
To: Satoru Takeuchi, linux-btrfs
On 2017/10/19 16:45, Satoru Takeuchi wrote:
> Some tools can select which superblock these commands use by "-s <superblock>"
> option. Although this option says the valid values are 0-2, we can set 3
> if filesystem is very large.
>
Hello,
Wiki says there are 4 superblocks. However in the implementation BTRFS_SUPER_MIROR_MAX
is 3 and 0 indicates the block at 64K (disk-io.h of btrfs-progs), therefore I think
there is no 4th superblock actually.
Regards,
Tomohiro
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] btrfs-progs: change mans to describe the third copy of superblock
2017-10-19 8:34 ` Misono, Tomohiro
@ 2017-10-19 9:05 ` Qu Wenruo
2017-10-19 9:38 ` Satoru Takeuchi
0 siblings, 1 reply; 4+ messages in thread
From: Qu Wenruo @ 2017-10-19 9:05 UTC (permalink / raw)
To: Misono, Tomohiro, Satoru Takeuchi, linux-btrfs
On 2017年10月19日 16:34, Misono, Tomohiro wrote:
> On 2017/10/19 16:45, Satoru Takeuchi wrote:
>> Some tools can select which superblock these commands use by "-s <superblock>"
>> option. Although this option says the valid values are 0-2, we can set 3
>> if filesystem is very large.
>>
>
> Hello,
> Wiki says there are 4 superblocks. However in the implementation BTRFS_SUPER_MIROR_MAX
> is 3 and 0 indicates the block at 64K (disk-io.h of btrfs-progs), therefore I think
> there is no 4th superblock actually.
Kernel implementation also shows that it will only update up to 3
superblocks:
---
if (max_mirrors == 0)
max_mirrors = BTRFS_SUPER_MIRROR_MAX;
for (i = 0; i < max_mirrors; i++) {
bytenr = btrfs_sb_offset(i);
if (bytenr + BTRFS_SUPER_INFO_SIZE >=
device->commit_total_bytes)
break;
---
And BTRFS_SUPER_MIRROR_MAX is 3:
---
#define BTRFS_SUPER_MIRROR_MAX 3
---
So even you can set any value and btrfs_sb_offset() can calculate the
super block offset, you will just read out some garbage.
Thanks,
Qu
>
> Regards,
> Tomohiro
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
>
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] btrfs-progs: change mans to describe the third copy of superblock
2017-10-19 9:05 ` Qu Wenruo
@ 2017-10-19 9:38 ` Satoru Takeuchi
0 siblings, 0 replies; 4+ messages in thread
From: Satoru Takeuchi @ 2017-10-19 9:38 UTC (permalink / raw)
To: Qu Wenruo; +Cc: Misono, Tomohiro, Satoru Takeuchi, linux-btrfs
At Thu, 19 Oct 2017 17:05:18 +0800,
Qu Wenruo wrote:
>
>
>
> On 2017年10月19日 16:34, Misono, Tomohiro wrote:
> > On 2017/10/19 16:45, Satoru Takeuchi wrote:
> >> Some tools can select which superblock these commands use by "-s <superblock>"
> >> option. Although this option says the valid values are 0-2, we can set 3
> >> if filesystem is very large.
> >>
> >
> > Hello,
> > Wiki says there are 4 superblocks. However in the implementation BTRFS_SUPER_MIROR_MAX
> > is 3 and 0 indicates the block at 64K (disk-io.h of btrfs-progs), therefore I think
> > there is no 4th superblock actually.
>
> Kernel implementation also shows that it will only update up to 3
> superblocks:
>
> ---
> if (max_mirrors == 0)
> max_mirrors = BTRFS_SUPER_MIRROR_MAX;
>
> for (i = 0; i < max_mirrors; i++) {
> bytenr = btrfs_sb_offset(i);
> if (bytenr + BTRFS_SUPER_INFO_SIZE >=
> device->commit_total_bytes)
> break;
> ---
>
> And BTRFS_SUPER_MIRROR_MAX is 3:
> ---
> #define BTRFS_SUPER_MIRROR_MAX 3
> ---
>
> So even you can set any value and btrfs_sb_offset() can calculate the
> super block offset, you will just read out some garbage.
My fault, sorry. I should read source more carefully. And thank you both
to let me know my mistake.
Thanks,
Satoru
>
> Thanks,
> Qu
> >
> > Regards,
> > Tomohiro
> >
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
> > the body of a message to majordomo@vger.kernel.org
> > More majordomo info at http://vger.kernel.org/majordomo-info.html
> >
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2017-10-19 7:45 [PATCH] btrfs-progs: change mans to describe the third copy of superblock Satoru Takeuchi
2017-10-19 8:34 ` Misono, Tomohiro
2017-10-19 9:05 ` Qu Wenruo
2017-10-19 9:38 ` Satoru Takeuchi
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