* uninit_bg compatibility?
@ 2010-09-21 13:28 Bo Brantén
2010-09-21 17:00 ` Andreas Dilger
2010-09-21 17:59 ` Ted Ts'o
0 siblings, 2 replies; 3+ messages in thread
From: Bo Brantén @ 2010-09-21 13:28 UTC (permalink / raw)
To: linux-ext4
Hello,
when writing new files to an ext4 file system using the Windows driver
fsck will later complain "Group descriptor nn checksum is invalid" and I
think that is because it used an yet unused block group without knowing
that they can be marked as uninitialized. So I thought a simple patch
would be to mount the file system read-only if that feature is in use
untill the driver is updated with full write support but I can't find the
flag to use, there is no EXT4_FEATURE_RO_COMPAT_UNINIT_BG so I thought I
ask here if anyone could clear this out.
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: uninit_bg compatibility?
2010-09-21 13:28 uninit_bg compatibility? Bo Brantén
@ 2010-09-21 17:00 ` Andreas Dilger
2010-09-21 17:59 ` Ted Ts'o
1 sibling, 0 replies; 3+ messages in thread
From: Andreas Dilger @ 2010-09-21 17:00 UTC (permalink / raw)
To: Bo Brantén; +Cc: linux-ext4
On 2010-09-21, at 06:28, Bo Brantén wrote:
> when writing new files to an ext4 file system using the Windows driver fsck will later complain "Group descriptor nn checksum is invalid" and I think that is because it used an yet unused block group without knowing that they can be marked as uninitialized. So I thought a simple patch would be to mount the file system read-only if that feature is in use untill the driver is updated with full write support but I can't find the flag to use, there is no EXT4_FEATURE_RO_COMPAT_UNINIT_BG so I thought I ask here if anyone could clear this out.
The Windows driver (or any driver for that matter) should ONLY allow read-only access if ANY feature in s_feature_ro_compat is unknown, and completely refuse to mount if any feature in s_feature_incompat is unknown.
The actual feature flag is called EXT4_FEATURE_RO_COMPAT_GDT_CSUM, but that doesn't matter, since what the code should be doing is masking off the features that it DOES understand and checking if any feature bits are remaining.
Cheers, Andreas
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^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: uninit_bg compatibility?
2010-09-21 13:28 uninit_bg compatibility? Bo Brantén
2010-09-21 17:00 ` Andreas Dilger
@ 2010-09-21 17:59 ` Ted Ts'o
1 sibling, 0 replies; 3+ messages in thread
From: Ted Ts'o @ 2010-09-21 17:59 UTC (permalink / raw)
To: Bo Brantén; +Cc: linux-ext4
On Tue, Sep 21, 2010 at 03:28:51PM +0200, Bo Brantén wrote:
>
> when writing new files to an ext4 file system using the Windows
> driver fsck will later complain "Group descriptor nn checksum is
> invalid" and I think that is because it used an yet unused block
> group without knowing that they can be marked as uninitialized. So I
> thought a simple patch would be to mount the file system read-only
> if that feature is in use untill the driver is updated with full
> write support but I can't find the flag to use, there is no
> EXT4_FEATURE_RO_COMPAT_UNINIT_BG so I thought I ask here if anyone
> could clear this out.
Yeah, this is one where we decided to change the feature to uninit_bg
(since that describes the net benefit to the end-user), but we never
ended up changing the name of the flag in the source code. The
feature flag in question is:
#define EXT4_FEATURE_RO_COMPAT_GDT_CSUM 0x0010
I'll note that the Windows driver must not be checking the feature
flags, since the whole point of RO_COMPAT flags is that if a file
system implementation (such as the Windows drivers) sees an RO_COMPAT
flag it doesn't understand, it's supposed to treat the file system as
read-only.
- Ted
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^ permalink raw reply [flat|nested] 3+ messages in thread
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2010-09-21 13:28 uninit_bg compatibility? Bo Brantén
2010-09-21 17:00 ` Andreas Dilger
2010-09-21 17:59 ` Ted Ts'o
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