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SubjectRe: [PATCH] ext2/3 as ext4

Hi!

> Hello Everyone,
> Below is a small patch I wrote for kernel version 2.6.31.6. It
> causes ext2/3 filesystems to be mounted using the ext4 driver, in a
> way that is transparent to the userspace (and kernelspace for that
> matter, as long as the code uses the kernel's mounting API) and
> requires no change to the userspace (/kernelspace). This patch is
> useful because: 1) It allows minimalist kernel fanatics, like myself,
> to drop 2 drivers from their builds without any loss in functionality.
> 2) It allows the ext2/3 filesystems to take advantage of the
> performance/general improvements in the ext4 driver. 3) In the future,
> with this patch, the ext2/3 driver code could be dropped from the
> kernel without any loss in functionality. I have been using this patch
> for 2 months now with no flaws on my home Linux box, which uses ext3
> drives on a daily basis.
>
> Let me know if you use this patch, if enough people use it I will
> write a proper KCONFIG and submit it for inclusion into the kernel.
>
> So without further ado, here is the patch.
>
> Sincerely,
> Philip Wernersbach <philip.wernersbach@gmail.com>

(I believe patch was whitespace damaged).

> --- linux-2.6.31.6.orig/fs/namespace.c 2009-11-28 22:30:07.178682500 -0500
> +++ linux-2.6.31.6/fs/namespace.c 2009-11-28 22:32:42.813462139 -0500
> @@ -6,6 +6,8 @@
> *
> * Based on code from fs/super.c, copyright Linus Torvalds and others.
> * Heavily rewritten.
> + *
> + * Uses ext2/3 as ext4 patch by Philip Wernersbach (November 2009)
> */
>

Add yourself to the CREDITS; we don't use comments for changelog these days.

> +/*
> + * compare_fs_names(char *fs1, char *fs2) - Part of the ext2/3 as ext4 patch
> + *
> + * The following is a standard string compare function, made to compare
> + * filesystem names, it returns 0 if they equal, and 1 if they do not.
> + * It only handles strings up to 255 characters though, so be cautious.
> + */
> +static int compare_fs_names(char *fs1, char *fs2)
> +{
> + int i;
> +
> + if (fs1 == 0L || fs2 == 0L) return 1;

Ouch?

> + for (i=0;i<256;i++)
> + {
> + if (fs1[i] != fs2[i])
> + return 1;
> + if (fs1[i] == 0 && fs2[i] == 0)
> + return 0;
> + if (fs1[i] == 0)
> + return 1;
> + if (fs2[i] == 0)
> + return 1;
> + }
> + return 0;

Can you use memcmp, instead?

> @@ -1891,6 +1921,22 @@
> struct path path;
> int retval = 0;
> int mnt_flags = 0;
> +
> + /*
> + * This causes ext2 filesystems to be mounted with the ext4 driver.
> + *
> + * Part of the ext2/3 as ext4 patch.
> + */
> + if (compare_fs_names(type_page, "ext2") == 0)
> + type_page[3] = '4';

Actualy strcmp() may be appropriate.

Pavel
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html


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