Re: [PATCH] ide-cd: Improve "weird block size" error message

[David Miller <davem@davemloft.net>]

From: Frans Pop <elendil@planet.nl>
Date: Tue, 23 Jun 2009 09:51:23 +0200

> In that case I'd like to propose the following patch. Currently the error
> can get printed much to frequently when there's a disc in the drive.
> Example:
> 
> Jun 13 18:06:28 gimli kernel: ide-cd: hdd: weird block size 2352
> Jun 13 18:06:28 gimli kernel: ide-cd: hdd: default to 2kb block size
> Jun 13 18:06:32 gimli kernel: ide-cd: hdd: weird block size 2352
> Jun 13 18:06:42 gimli kernel: ide-cd: hdd: default to 2kb block size

Thinking about this a bit.  Let's look at what problem this is
trying to avoid, as per the commit message:

--------------------
    ide-cd: fix oops when using growisofs
    
    cdrom_read_capacity() will blindly return the capacity from the device
    without sanity-checking it.  This later causes code in fs/buffer.c to
    oops.
    
    Fix this by checking that the device is telling us sensible things.
--------------------

Well, for the values Frans's CDROM is giving, this OOPS would not
take place and the weird sector value is completely harmless.

Since SECTOR_BITS is 9:

(2352 >> 9) == (2048 >> 9) == 4

There is simply no benefit from this warning in this situation.

Therefore, any objections to something like this?

ide-cd: Don't warn on bogus block size unless it actually matters.

Frans Pop reported that his CDROM drive reports a blocksize of 2352,
and this causes new warnings due to commit
e8e7b9eb11c34ee18bde8b7011af41938d1ad667 ("ide-cd: fix oops when using
growisofs").

What we're trying to do is make sure that "blocklen >> SECTOR_BITS"
is something the block layer won't choke on.

And for Frans case "2352 >> SECTOR_BITS" is equal to
"2048 >> SECTOR_BITS", and thats "4".

So warning in this case gives no real benefit.

Reported-by: Frans Pop <elendil@planet.nl>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/ide/ide-cd.c b/drivers/ide/ide-cd.c
index 4a19686..a9a1bfb 100644
--- a/drivers/ide/ide-cd.c
+++ b/drivers/ide/ide-cd.c
@@ -876,9 +876,12 @@ static int cdrom_read_capacity(ide_drive_t *drive, unsigned long *capacity,
 		return stat;
 
 	/*
-	 * Sanity check the given block size
+	 * Sanity check the given block size, in so far as making
+	 * sure the sectors_per_frame we give to the caller won't
+	 * end up being bogus.
 	 */
 	blocklen = be32_to_cpu(capbuf.blocklen);
+	blocklen = (blocklen >> SECTOR_BITS) << SECTOR_BITS;
 	switch (blocklen) {
 	case 512:
 	case 1024: