linux-kernel - Re: [PATCH, RESEND] tmpfs: fix mounts when size is less than the page size

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Message-ID: <c0526ddf0711041012x7b41269x12a05ddb6e03a04d@mail.gmail.com>
Date:	Sun, 4 Nov 2007 11:12:22 -0700
From:	"Michael Marineau" <mike@...ineau.org>
To:	"Hugh Dickins" <hugh@...itas.com>
Cc:	"Andrew Morton" <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, trivial@...nel.org
Subject: Re: [PATCH, RESEND] tmpfs: fix mounts when size is less than the page size

On 11/4/07, Hugh Dickins <hugh@...itas.com> wrote:
> Fair enough, that does match the documentation of "size=0" better.
> Though either way, someone who typos is going to get one kind of surprise
> or another.  Do you mind if we do it slightly differently, achieving the
> same effect without a special case, by rounding up instead of down?

Sounds reasonable to me. I didn't know about DIV_ROUND_UP :-)

>
>
> From: Michael Marineau <mike@...ineau.org>
>
> When tmpfs is mounted with a size less than one page, the number of blocks
> is set to 0 which makes the tmpfs mount unlimited. This can lead to a quick
> and surprising death if someone typos a tmpfs mount command and writes too
> much.
>
> tmpfs can still be mounted as unlimited if size or nr_blocks is exactly 0,
> as Documentation/filesystems/tmpfs.txt says.
>
> Hugh: do this by rounding size up instead of down in all cases: which
> slightly expands other odd-sized tmpfs mounts, but in a consistent way.
>
> Signed-off-by: Michael Marineau <mike@...ineau.org>
> Signed-off-by: Hugh Dickins <hugh@...itas.com>
> ---
>
>  mm/shmem.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> --- 2.6.24-rc1-git/mm/shmem.c   2007-10-31 06:18:05.000000000 +0000
> +++ linux/mm/shmem.c    2007-11-04 11:46:09.000000000 +0000
> @@ -2137,7 +2137,7 @@ static int shmem_parse_options(char *opt
>                         }
>                         if (*rest)
>                                 goto bad_val;
> -                       *blocks = size >> PAGE_CACHE_SHIFT;
> +                       *blocks = DIV_ROUND_UP(size, PAGE_CACHE_SIZE);
>                 } else if (!strcmp(this_char,"nr_blocks")) {
>                         *blocks = memparse(value,&rest);
>                         if (*rest)
>


-- 
Michael Marineau
Oregon State University
mike@...ineau.org
-
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