package/mtd/mtd-large-writes.patch

From fa0923bc3f33ee4a4a381fd072baf67e0728153a Mon Sep 17 00:00:00 2001
From: Denton Gentry <dgentry@google.com>
Date: Thu, 28 Jun 2012 22:51:01 -0700
Subject: [PATCH] Avoid kmalloc errors for large writes.

Patch from http://patchwork.ozlabs.org/patch/140766/

Original description by Brian Norris <computersforpeace@gmail.com>:
ioctl(MEMWRITE) is implemented with memdup_user(), and so it allocates
kernel memory in contiguous regions. This limits its usefulness for large
amounts of data, since contiguous kernel memory can become scarce. I have
experienced "out of memory" problems with ubiformat, for instance, which
writes in eraseblock-sized regions:

  ...
  ubiformat: flashing eraseblock 12 -- 72 % complete
  ubiformat: page allocation failure.
  order:8, mode:0xd0
  Call Trace:
  [<8043fa7c>] dump_stack+0x8/0x34
  [<8008c940>] __alloc_pages_nodemask+0x408/0x618
  [<800bd748>] cache_alloc_refill+0x400/0x730
  [<800bdbbc>] __kmalloc+0x144/0x154
  [<8009cae4>] memdup_user+0x24/0x94
  [<802d04e4>] mtd_ioctl+0xba8/0xbd0
  [<802d0544>] mtd_unlocked_ioctl+0x38/0x5c
  [<800d43c0>] do_vfs_ioctl+0xa4/0x6e4
  [<800d4a44>] sys_ioctl+0x44/0xa0
  [<8000f95c>] stack_done+0x20/0x40
  ...
  libmtd: error!: MEMWRITE ioctl failed for eraseblock 12 (mtd0)
          error 12 (Cannot allocate memory)
  ubiformat: error!: cannot write eraseblock 12
             error 12 (Cannot allocate memory)

This error can be mitigated for now by only using ioctl(MEMWRITE) when we
need to write OOB data, since we can only do this in small transactions
anyway. Then, data-only transactions (like those originating from
ubiformat) can be carried out with write() calls.

This issue can also be solved within the kernel ioctl(), but either way,
this patch is still useful, since write() is more straightforward (and
efficient?) than ioctl() for data-only writes.
---
 lib/libmtd.c |   28 ++++++++++++++--------------
 1 file changed, 14 insertions(+), 14 deletions(-)

diff --git a/lib/libmtd.c b/lib/libmtd.c
index 9b247ae..054f4c0 100644
--- a/lib/libmtd.c
+++ b/lib/libmtd.c
@@ -1141,21 +1141,21 @@ int mtd_write(libmtd_t desc, const struct mtd_dev_info *mtd, int fd, int eb,
 	/* Calculate seek address */
 	seek = (off_t)eb * mtd->eb_size + offs;
 
-	ops.start = seek;
-	ops.len = len;
-	ops.ooblen = ooblen;
-	ops.usr_data = (uint64_t)(unsigned long)data;
-	ops.usr_oob = (uint64_t)(unsigned long)oob;
-	ops.mode = mode;
-
-	ret = ioctl(fd, MEMWRITE, &ops);
-	if (ret == 0)
-		return 0;
-	else if (errno != ENOTTY && errno != EOPNOTSUPP)
-		return mtd_ioctl_error(mtd, eb, "MEMWRITE");
-
-	/* Fall back to old methods if necessary */
 	if (oob) {
+		ops.start = seek;
+		ops.len = len;
+		ops.ooblen = ooblen;
+		ops.usr_data = (uint64_t)(unsigned long)data;
+		ops.usr_oob = (uint64_t)(unsigned long)oob;
+		ops.mode = mode;
+
+		ret = ioctl(fd, MEMWRITE, &ops);
+		if (ret == 0)
+			return 0;
+		else if (errno != ENOTTY && errno != EOPNOTSUPP)
+			return mtd_ioctl_error(mtd, eb, "MEMWRITE");
+
+		/* Fall back to old OOB ioctl() if necessary */
 		if (mode == MTD_OPS_AUTO_OOB)
 			if (legacy_auto_oob_layout(mtd, fd, ooblen, oob))
 				return -1;
-- 
1.7.9.4