libmtd: fix mtd_write() issues for large data-only writes

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 files changed, 14 insertions(+), 14 deletions(-)

index fb4586c..c4836df 100644
@@ -1147,21 +1147,21 @@ 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;

1.7.5.4

Pushed this one and the other 3 patches to mtd-utils.git, thanks a lot!

Best Regards,
Artem Bityutskiy

Thanks for the push! Please note that there are still two patches outstanding, that you said you pushed earlier but are not in the repository AFAICT. They were in another thread, with subjects:

[PATCH 1/3] libmtd: perform device checking first [PATCH 2/3] libmtd_legacy: don't open device in R/W

Sorry for the confusion. I can resend if needed.

Thanks,
Brian

Pushed those 2, thanks!

Best Regards,
Artem Bityutskiy