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

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Date:	Sun, 4 Nov 2007 12:19:26 +0000 (GMT)
From:	Hugh Dickins <hugh@...itas.com>
To:	Michael Marineau <mike@...ineau.org>
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

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?

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)
-
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