[PATCH] block: Add Kconfig help which notes that ext4 needs CONFIG_LSF

[PATCH] block: Add Kconfig help which notes that ext4 needs CONFIG_LSF

[Theodore Ts'o]

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: Jens Axboe <jens.axboe@oracle.com>
---
 block/Kconfig |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/block/Kconfig b/block/Kconfig
index 1ab7c15..e10f4c1 100644
--- a/block/Kconfig
+++ b/block/Kconfig
@@ -64,6 +64,12 @@ config LSF
 	  Say Y here if you want to be able to handle very large files (2TB
 	  and larger), otherwise say N.
 
+	  The ext4 filesystem requires that this feature be enabled in
+	  order to support filesystems that have the huge_file feature
+	  enabled.    Otherwise, it will refuse to mount any filesystems
+	  that use the huge_file feature, which is enabled by default
+	  by mke2fs.ext4.
+
 	  If unsure, say Y.
 
 config BLK_DEV_BSG
-- 
1.6.0.4.8.g36f27.dirty

Re: [PATCH] block: Add Kconfig help which notes that ext4 needs CONFIG_LSF

[Theodore Tso]

I had to use a slightly different patch for 2.6.28-git7...

block: Add Kconfig help which notes that ext4 needs CONFIG_LBD

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: Jens Axboe <jens.axboe@oracle.com>
diff --git a/block/Kconfig b/block/Kconfig
index ac0956f..0cbb3b8 100644
--- a/block/Kconfig
+++ b/block/Kconfig
@@ -36,6 +36,12 @@ config LBD
 	  This option also enables support for single files larger than
 	  2TB.
 
+	  The ext4 filesystem requires that this feature be enabled in
+	  order to support filesystems that have the huge_file feature
+	  enabled.    Otherwise, it will refuse to mount any filesystems
+	  that use the huge_file feature, which is enabled by default
+	  by mke2fs.ext4.   The GFS2 filesystem also requires this feature.
+
 	  If unsure, say N.
 
 config BLK_DEV_IO_TRACE

Re: [PATCH] block: Add Kconfig help which notes that ext4 needs CONFIG_LSF

[Andreas Dilger]

On Jan 06, 2009  12:21 -0500, Theodore Ts'o wrote:
> @@ -64,6 +64,12 @@ config LSF
> +	  The ext4 filesystem requires that this feature be enabled in
> +	  order to support filesystems that have the huge_file feature
> +	  enabled.    Otherwise, it will refuse to mount any filesystems
> +	  that use the huge_file feature, which is enabled by default
> +	  by mke2fs.ext4.

Wouldn't it make sense to just enable this by default if ext4 is enabled?

On a related note, I wonder if we need to re-examine the use of the COMPAT
flags in ext4.  We went from a usage of "kernel enables flag when feature
is used" (e.g. LARGE_FILE) to "admin must set flag in order to use feature"
(e.g HUGE_FILE).

The former system was recording the state of currently-used features in the
filesystem, and maximized portability of the filesystem if the feature
was NOT used.  The newer system makes a filesystem somewhat less portable
even if the feature is not being used at all (e.g. files > 2TB in size).

I wonder if we should split the s_feature_*compat fields in the superblock
to "present feature" and "allowed feature" so that e.g. HUGE_FILE count
be put into "allowed feature" and would only appear in "present feature"
if a file > 2TB in size arrives.  That ensures the filesystem remains
maximally compatible, while allowing the admin to select which features
are permissible.

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.

Re: [PATCH] block: Add Kconfig help which notes that ext4 needs CONFIG_LSF

[Jens Axboe]

On Thu, Jan 08 2009, Andreas Dilger wrote:
> On Jan 06, 2009  12:21 -0500, Theodore Ts'o wrote:
> > @@ -64,6 +64,12 @@ config LSF
> > +	  The ext4 filesystem requires that this feature be enabled in
> > +	  order to support filesystems that have the huge_file feature
> > +	  enabled.    Otherwise, it will refuse to mount any filesystems
> > +	  that use the huge_file feature, which is enabled by default
> > +	  by mke2fs.ext4.
> 
> Wouldn't it make sense to just enable this by default if ext4 is enabled?

Agree, since it'll prevent the fs from mounting, using a select makes a
lot more sense.

-- 
Jens Axboe