[Qemu-devel] QEMU SD card emulation problem

[Taimoor Mirza]

Hi Guys,

I have been trying to use SD card emulation of QEMU by providing host
directory to QEMU to treat it as SD card. For this I am using option
"-sd fat:16:rw:/home/taimoor/temp/sdcard". This works fine for me and
I can see list of files in guest system.
But when I delete some file from guest system sdcard directory and
then try adding new file there, I get following error:

Could not open /home/taimoor/temp/sdcard... (Is a directory, 21) Error
handling commits (-3)

I have debugged QEMU and have found that error is coming from open
function call in qemu_open function that is called from
commit_one_file call from ACTION_WRITEOUT case in handle_commits.

Backtrace is:

(gdb) bt
#0  qemu_open (name=0x80c7a8c0 "/home/taimoor/temp/sdcard", flags=66)
at util/osdep.c:202
#1  0x80091dc1 in commit_one_file (s=0x80c7e3e0, dir_index=4,
offset=0) at block/vvfat.c:2325
#2  0x800927b9 in handle_commits (s=0x80c7e3e0) at block/vvfat.c:2588
#3  0x80092cb1 in do_commit (s=0x80c7e3e0) at block/vvfat.c:2736
#4  0x80092df2 in try_commit (s=0x80c7e3e0) at block/vvfat.c:2766
#5  0x8009335a in vvfat_write (bs=0x80c7d258, sector_num=64,
buf=0x80e1e000 "\370\377\377\377\377\377\004", nb_sectors=1) at
block/vvfat.c:2860
#6  0x800933f1 in vvfat_co_write (bs=0x80c7d258, sector_num=64,
buf=0x80e1e000 "\370\377\377\377\377\377\004", nb_sectors=1) at
block/vvfat.c:2872
#7  0x80052898 in bdrv_aio_rw_vector (bs=0x80c7d258, sector_num=64,
qiov=0xb50869b4, nb_sectors=1, cb=0x800530fe <bdrv_co_io_em_complete>,
opaque=0xb5ceccf0, is_write=1) at block.c:4065
#8  0x80052a01 in bdrv_aio_writev_em (bs=0x80c7d258, sector_num=64,
qiov=0xb50869b4, nb_sectors=1, cb=0x800530fe <bdrv_co_io_em_complete>,
opaque=0xb5ceccf0) at block.c:4086
#9  0x800531fd in bdrv_co_io_em (bs=0x80c7d258, sector_num=64,
nb_sectors=1, iov=0xb50869b4, is_write=true) at block.c:4283
#10 0x8005336d in bdrv_co_writev_em (bs=0x80c7d258, sector_num=64,
nb_sectors=1, iov=0xb50869b4) at block.c:4310
#11 0x8004e772 in bdrv_co_do_writev (bs=0x80c7d258, sector_num=64,
nb_sectors=1, qiov=0xb50869b4, flags=0) at block.c:2625
#12 0x8004e8b9 in bdrv_co_writev (bs=0x80c7d258, sector_num=64,
nb_sectors=1, qiov=0xb50869b4) at block.c:2650
#13 0x8007a59d in raw_co_writev (bs=0x80c7b8c0, sector_num=64,
nb_sectors=1, qiov=0xb50869b4) at block/raw.c:31
#14 0x8004e772 in bdrv_co_do_writev (bs=0x80c7b8c0, sector_num=64,
nb_sectors=1, qiov=0xb50869b4, flags=0) at block.c:2625
#15 0x8004d40a in bdrv_rw_co_entry (opaque=0xb508692c) at block.c:2175
#16 0x8009978c in coroutine_trampoline (i0=-2134407824, i1=0) at
coroutine-ucontext.c:118
#17 0x0059482b in makecontext () at
../sysdeps/unix/sysv/linux/i386/makecontext.S:88
#18 0x80c78570 in ?? ()
#19 0x00008124 in ?? ()
#20 0x00000001 in ?? ()
#21 0x00000000 in ?? ()


Few questions of mine are:
1) Is it problem with using directory with -sd option? I have seen
that most of ppl. use -sd with SD card image file?
2) Why WRITE_THROUGH action only calls commit_one_file that looks to
be handling only single file commits?
3) Is SD card emulation stable or its known to be broken?

Thanks,
Taimoor