brd: fix ramdisk regression

From: Marcin Krol <[email protected]>

In 2.6.25, ramdisk devices show up in /proc/partitions, which is a behaviour change from the old rd.c. Add GENHD_FL_SUPPRESS_PARTITION_INFO, which was present in rd.c.

Signed-off-by Marcin Krol <[email protected]>

drivers/block/brd.c line 448

Quoted 10 lines

drivers/block/brd.c renamed from drivers/block/brd.c.orig +1 -0

@@ -442,6 +442,7 @@
 	disk->fops		= &brd_fops;
 	disk->private_data	= brd;
 	disk->queue		= brd->brd_queue;
+	disk->flags |= GENHD_FL_SUPPRESS_PARTITION_INFO;
 	sprintf(disk->disk_name, "ram%d", i);
 	set_capacity(disk, rd_size * 2);
 

Why is it a "regression"?

The change in 2.6.25 was a back-compatible one.

This change is not a back-compatible one and if we're going to now withdraw the newly-added 2.6.25 feature then we should also withdraw it from 2.6.26.x and 2.6.25.x (if that is still under maintenance). To reduce the incidence of "hey where did my feature go" problems.

Really, life would be simpler if we just left the accidentally-added feature in place. What problems does it cause?

Quoted 15 lines

drivers/block/brd.c line 448

Quoted 10 lines

drivers/block/brd.c renamed from drivers/block/brd.c.orig +1 -0

@@ -442,6 +442,7 @@
 	disk->fops		= &brd_fops;
 	disk->private_data	= brd;
 	disk->queue		= brd->brd_queue;
+	disk->flags |= GENHD_FL_SUPPRESS_PARTITION_INFO;
 	sprintf(disk->disk_name, "ram%d", i);
 	set_capacity(disk, rd_size * 2);
 

Why is it a "regression"?

The change in 2.6.25 was a back-compatible one.

Quoted 7 lines

This change is not a back-compatible one and if we're going to now withdraw the newly-added 2.6.25 feature then we should also withdraw it from 2.6.26.x and 2.6.25.x (if that is still under maintenance). To reduce the incidence of "hey where did my feature go" problems.

Really, life would be simpler if we just left the accidentally-added feature in place. What problems does it cause?

All kernels prior to 2.6.25 weren't displaying ramdisks in /proc/partitions. Since there are many userspace tools using infromation from /proc/partitions some of them may now behave incorrectly (I didn't tested any though). For example before 2.6.25 /proc/partitions was empty if no block devices like hard disks and such were detected by kernel. Now all 16 ramdisks are always visible there. Some software may rely on such information (I mean, on empty /proc/partitions).

There was quite similar situation back in 2004, and ramdisks were excluded back from displaying. Thats why I called this a regression (maybe a bit unfortunate). See this patch for info:
http://kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.3-rc2/2.6.3-rc2-mm1/broken-out/nbd-proc-partitions-fix.patch

I also think that someone somewhere (long time ago) excluded ramdisks from /proc/partitions for good reasons. It is possible that now such new "feature" is harmless, but I think there are more chances that someone will say "hey, /proc/partitions has changed, now my software doesn't work" then "hey where did my new 2.6.25 feature go". nbd devices are also excluded, maybe for very same (unknown to me) reasons.

For me this change isn't problematic. Yes, it did broken my software and yes, I could fix my software but since its working only on specific kernels (precompiled by me) I've chosen to revert kernel change instead to get old behaviour.

Quoted 4 lines

For me this change isn't problematic. Yes, it did broken my software and yes, I could fix my software but since its working only on specific kernels (precompiled by me) I've chosen to revert kernel change instead to get old behaviour.

Ah, it only affects 2.6.25.x and no earlier -stable kernels. Not so bad.

Greg, Chris? Thoughts?