[PATCH] ubi: Speedup ubi_io_read_vid_hdr()

[Richard Weinberger]

Currently we read a whole (sub)page from flash when reading
the VID header.
Sascha reported that reading only UBI_VID_HDR_SIZE instead
gives him a decent speedup during a full scan.

Since we have to obey shifted headers too we have to read
ubi->vid_hdr_shift + UBI_VID_HDR_SIZE bytes.
It is also important to set the buffer to 0xff bytes before
reading as in ubi_io_write_vid_hdr() the whole (sub)page
is written back to flash and we cannot risk leaking
kernel memory into the storage medium.

Reported-by: Sascha Hauer <s.hauer at pengutronix.de>
Signed-off-by: Richard Weinberger <richard at nod.at>
---
Sascha,

can you please this patch a try?

Thanks,
//richard
---
 drivers/mtd/ubi/io.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/mtd/ubi/io.c b/drivers/mtd/ubi/io.c
index 10cf3b5..803a22d 100644
--- a/drivers/mtd/ubi/io.c
+++ b/drivers/mtd/ubi/io.c
@@ -1018,8 +1018,9 @@ int ubi_io_read_vid_hdr(struct ubi_device *ubi, int pnum,
 	ubi_assert(pnum >= 0 &&  pnum < ubi->peb_count);
 
 	p = (char *)vid_hdr - ubi->vid_hdr_shift;
+	memset(p, 0xff, ubi->vid_hdr_alsize);
 	read_err = ubi_io_read(ubi, p, pnum, ubi->vid_hdr_aloffset,
-			  ubi->vid_hdr_alsize);
+			  ubi->vid_hdr_shift + UBI_VID_HDR_SIZE);
 	if (read_err && read_err != UBI_IO_BITFLIPS && !mtd_is_eccerr(read_err))
 		return read_err;
 
-- 
2.7.3