Re: [Qemu-devel] [PATCH] m25p80: fix test on blk_pread() return value

["Cédric Le Goater" <clg@kaod.org>]

>> #4  0x00007fa81c6694ac in bdrv_aligned_pwritev (bs=0x7fa81d4dd050, req=<optimized out>, offset=30878208, 
>>     bytes=512, qiov=0x7fa7f47fee60, flags=0)
>>     at /home/legoater/work/qemu/qemu-ast2400-mainline.git/block/io.c:1243
>> #5  0x00007fa81c669ecb in bdrv_co_pwritev (bs=0x7fa81d4dd050, offset=8, bytes=512, qiov=0x7fa80d5191c0, 
>>     flags=(BDRV_REQ_COPY_ON_READ | BDRV_REQ_ZERO_WRITE | BDRV_REQ_MAY_UNMAP | BDRV_REQ_NO_SERIALISING | BDRV_REQ_FUA | unknown: 4278124256), flags@entry=(unknown: 0))
>>     at /home/legoater/work/qemu/qemu-ast2400-mainline.git/block/io.c:1492
> 
> That 'flags' value looks bogus...
> 
>> #6  0x00007fa81c65e367 in blk_co_pwritev (blk=0x7fa81d4c5b60, offset=30878208, bytes=256, qiov=0x7fa80d5191c0, 
>>     flags=(unknown: 0)) at /home/legoater/work/qemu/qemu-ast2400-mainline.git/block/block-backend.c:788
>> #7  0x00007fa81c65e49b in blk_aio_write_entry (opaque=0x7fa7e849aca0)
>>     at /home/legoater/work/qemu/qemu-ast2400-mainline.git/block/block-backend.c:977
>> #8  0x00007fa81c6c823a in coroutine_trampoline (i0=<optimized out>, i1=<optimized out>)
>>     at /home/legoater/work/qemu/qemu-ast2400-mainline.git/util/coroutine-ucontext.c:78
>> #9  0x00007fa818ea8f00 in ?? () from /lib/x86_64-linux-gnu/libc.so.6
> 
> and we don't get anything further in the backtrace beyond coroutines, to
> see who's sending the bad parameters.  I recently debugged a bogus flags
> in bdrv_aio_preadv, by hoisting an assert to occur before coroutines are
> used in blk_aio_prwv():
> 
> https://lists.gnu.org/archive/html/qemu-devel/2016-06/msg02948.html
> 
> I've just posted v2 of that patch (now a 2/2 series), but in v2 no
> longer kept the assert at that point.  But maybe the correct fix, and/or
> the hack for catching the bug prior to coroutines, will help you debug
> where the bad arguments are coming from.

That does not fix the assert.
 
>> #10 0x00007fa80d5189d0 in ?? ()
>> #11 0x0000000000000000 in ?? ()
>> (gdb) up 4
>> #4  0x00007fa81c6694ac in bdrv_aligned_pwritev (bs=0x7fa81d4dd050, req=<optimized out>, offset=30878208, 
>>     bytes=512, qiov=0x7fa7f47fee60, flags=0)
>>     at /home/legoater/work/qemu/qemu-ast2400-mainline.git/block/io.c:1243
>> 1243	    assert(!qiov || bytes == qiov->size);
>> (gdb) p *qiov 
>> $1 = {iov = 0x7fa81da671d0, niov = 1, nalloc = 1, size = 256}

So, it seems that the issue is coming from the fact that bdrv_co_pwritev()
does not handle alignments less than BDRV_SECTOR_SIZE :

	/* TODO Lift BDRV_SECTOR_SIZE restriction in BlockDriver interface */
	uint64_t align = MAX(BDRV_SECTOR_SIZE, bs->request_alignment);

It calls bdrv_aligned_pwritev() which does the assert : 

	assert(!qiov || bytes == qiov->size);


This is because flash_sync_page(), in m25p80.c, now writes with a len of 
0x100, which the page size in flash modules. commit 243e6f69c129 
("m25p80: Switch to byte-based block access") removed the alignment on 
BDRV_SECTOR_SIZE. 

So I think the safest is to restore the alignment on writes. see below.
If this is ok, I will send a little serie of fixes for m25p80 with this 
one included.

Thanks,

C. 

From: Cédric Le Goater <clg@kaod.org>
Subject: [PATCH] m25p80: restore BDRV_SECTOR_SIZE alignment on writes
Date: Tue, 14 Jun 2016 09:32:22 +0200
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commit 243e6f69c129 ("m25p80: Switch to byte-based block access")
removed the alignment of writes on BDRV_SECTOR_SIZE, so they are
now done on a page size (0x100) basis. This is not supported by the
bdrv routines which asserts in bdrv_aligned_pwritev() :

    assert(!qiov || bytes == qiov->size);

bytes being rounded up to BDRV_SECTOR_SIZE and qiov->size == 0x100

Signed-off-by: Cédric Le Goater <clg@kaod.org>
---
 hw/block/m25p80.c |   18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

Index: qemu-ast2400-mainline.git/hw/block/m25p80.c
===================================================================
--- qemu-ast2400-mainline.git.orig/hw/block/m25p80.c
+++ qemu-ast2400-mainline.git/hw/block/m25p80.c
@@ -359,21 +359,25 @@ static void blk_sync_complete(void *opaq
 
 static void flash_sync_page(Flash *s, int page)
 {
+    int blk_sector, nb_sectors;
     QEMUIOVector iov;
 
     if (!s->blk || blk_is_read_only(s->blk)) {
         return;
     }
 
+    blk_sector = (page * s->pi->page_size) / BDRV_SECTOR_SIZE;
+    nb_sectors = DIV_ROUND_UP(s->pi->page_size, BDRV_SECTOR_SIZE);
     qemu_iovec_init(&iov, 1);
-    qemu_iovec_add(&iov, s->storage + page * s->pi->page_size,
-                   s->pi->page_size);
-    blk_aio_pwritev(s->blk, page * s->pi->page_size, &iov, 0,
+    qemu_iovec_add(&iov, s->storage + blk_sector * BDRV_SECTOR_SIZE,
+                   nb_sectors * BDRV_SECTOR_SIZE);
+    blk_aio_pwritev(s->blk, blk_sector * BDRV_SECTOR_SIZE, &iov, 0,
                     blk_sync_complete, NULL);
 }
 
 static inline void flash_sync_area(Flash *s, int64_t off, int64_t len)
 {
+    int64_t start, end, nb_sectors;
     QEMUIOVector iov;
 
     if (!s->blk || blk_is_read_only(s->blk)) {
@@ -381,9 +385,13 @@ static inline void flash_sync_area(Flash
     }
 
     assert(!(len % BDRV_SECTOR_SIZE));
+    start = off / BDRV_SECTOR_SIZE;
+    end = (off + len) / BDRV_SECTOR_SIZE;
+    nb_sectors = end - start;
     qemu_iovec_init(&iov, 1);
-    qemu_iovec_add(&iov, s->storage + off, len);
-    blk_aio_pwritev(s->blk, off, &iov, 0, blk_sync_complete, NULL);
+    qemu_iovec_add(&iov, s->storage + (start * BDRV_SECTOR_SIZE),
+                                        nb_sectors * BDRV_SECTOR_SIZE);
+    blk_aio_pwritev(s->blk, start, &iov, 0, blk_sync_complete, NULL);
 }
 
 static void flash_erase(Flash *s, int offset, FlashCMD cmd)