From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=44076 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1PgGEf-0003S3-0t for qemu-devel@nongnu.org; Fri, 21 Jan 2011 07:37:01 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1PgGEd-0000rc-KF for qemu-devel@nongnu.org; Fri, 21 Jan 2011 07:37:00 -0500 Received: from mail-wy0-f173.google.com ([74.125.82.173]:37154) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1PgGEd-0000rA-Cb for qemu-devel@nongnu.org; Fri, 21 Jan 2011 07:36:59 -0500 Received: by wyg36 with SMTP id 36so1792870wyg.4 for ; Fri, 21 Jan 2011 04:36:58 -0800 (PST) MIME-Version: 1.0 Sender: tamura.yoshiaki@gmail.com In-Reply-To: <4D397C8E.7080703@redhat.com> References: <1295449188-17877-1-git-send-email-Pierre.Riteau@irisa.fr> <04350B7C-9933-4A70-8FA9-B5B409D1E10A@irisa.fr> <43211019-BF0D-405A-99B7-54C9B3BBE58E@irisa.fr> <4D397C8E.7080703@redhat.com> Date: Fri, 21 Jan 2011 21:36:58 +0900 Message-ID: Subject: Re: [Qemu-devel] [PATCH] Fix block migration when the device size is not a multiple of 1 MB From: Yoshiaki Tamura Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Kevin Wolf Cc: "qemu-devel@nongnu.org" , Pierre Riteau 2011/1/21 Kevin Wolf : > Am 21.01.2011 13:15, schrieb Yoshiaki Tamura: >> 2011/1/21 Pierre Riteau : >>> Le 20 janv. 2011 =E0 17:18, Yoshiaki Tamura a =E9crit : >>> >>>> 2011/1/20 Pierre Riteau : >>>>> On 20 janv. 2011, at 03:06, Yoshiaki Tamura wrote: >>>>> >>>>>> 2011/1/19 Pierre Riteau : >>>>>>> b02bea3a85cc939f09aa674a3f1e4f36d418c007 added a check on the retur= n >>>>>>> value of bdrv_write and aborts migration when it fails. However, if= the >>>>>>> size of the block device to migrate is not a multiple of BLOCK_SIZE >>>>>>> (currently 1 MB), the last bdrv_write will fail with -EIO. >>>>>>> >>>>>>> Fixed by calling bdrv_write with the correct size of the last block= . >>>>>>> --- >>>>>>> =A0block-migration.c | =A0 16 +++++++++++++++- >>>>>>> =A01 files changed, 15 insertions(+), 1 deletions(-) >>>>>>> >>>>>>> diff --git a/block-migration.c b/block-migration.c >>>>>>> index 1475325..eeb9c62 100644 >>>>>>> --- a/block-migration.c >>>>>>> +++ b/block-migration.c >>>>>>> @@ -635,6 +635,8 @@ static int block_load(QEMUFile *f, void *opaque= , int version_id) >>>>>>> =A0 =A0 int64_t addr; >>>>>>> =A0 =A0 BlockDriverState *bs; >>>>>>> =A0 =A0 uint8_t *buf; >>>>>>> + =A0 =A0int64_t total_sectors; >>>>>>> + =A0 =A0int nr_sectors; >>>>>>> >>>>>>> =A0 =A0 do { >>>>>>> =A0 =A0 =A0 =A0 addr =3D qemu_get_be64(f); >>>>>>> @@ -656,10 +658,22 @@ static int block_load(QEMUFile *f, void *opaq= ue, int version_id) >>>>>>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 return -EINVAL; >>>>>>> =A0 =A0 =A0 =A0 =A0 =A0 } >>>>>>> >>>>>>> + =A0 =A0 =A0 =A0 =A0 =A0total_sectors =3D bdrv_getlength(bs) >> BD= RV_SECTOR_BITS; >>>>>>> + =A0 =A0 =A0 =A0 =A0 =A0if (total_sectors <=3D 0) { >>>>>>> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0fprintf(stderr, "Error getting len= gth of block device %s\n", device_name); >>>>>>> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0return -EINVAL; >>>>>>> + =A0 =A0 =A0 =A0 =A0 =A0} >>>>>>> + >>>>>>> + =A0 =A0 =A0 =A0 =A0 =A0if (total_sectors - addr < BDRV_SECTORS_PE= R_DIRTY_CHUNK) { >>>>>>> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0nr_sectors =3D total_sectors - add= r; >>>>>>> + =A0 =A0 =A0 =A0 =A0 =A0} else { >>>>>>> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0nr_sectors =3D BDRV_SECTORS_PER_DI= RTY_CHUNK; >>>>>>> + =A0 =A0 =A0 =A0 =A0 =A0} >>>>>>> + >>>>>>> =A0 =A0 =A0 =A0 =A0 =A0 buf =3D qemu_malloc(BLOCK_SIZE); >>>>>>> >>>>>>> =A0 =A0 =A0 =A0 =A0 =A0 qemu_get_buffer(f, buf, BLOCK_SIZE); >>>>>>> - =A0 =A0 =A0 =A0 =A0 =A0ret =3D bdrv_write(bs, addr, buf, BDRV_SEC= TORS_PER_DIRTY_CHUNK); >>>>>>> + =A0 =A0 =A0 =A0 =A0 =A0ret =3D bdrv_write(bs, addr, buf, nr_secto= rs); >>>>>>> >>>>>>> =A0 =A0 =A0 =A0 =A0 =A0 qemu_free(buf); >>>>>>> =A0 =A0 =A0 =A0 =A0 =A0 if (ret < 0) { >>>>>>> -- >>>>>>> 1.7.3.5 >>>>>>> >>>>>>> >>>>>>> >>>>>> >>>>>> Hi Pierre, >>>>>> >>>>>> I don't think the fix above is correct. =A0If you have a file which >>>>>> isn't aliened with BLOCK_SIZE, you won't get an error with the >>>>>> patch. =A0However, the receiver doesn't know how much sectors which >>>>>> the sender wants to be written, so the guest may fail after >>>>>> migration because some data may not be written. =A0IIUC, although >>>>>> changing bytestream should be prevented as much as possible, we >>>>>> should save/load total_sectors to check appropriate file is >>>>>> allocated on the receiver side. >>>>> >>>>> Isn't the guest supposed to be started using a file with the correct = size? >>>> >>>> I personally don't like that; It's insisting too much to the user. >>>> Can't we expand the image on the fly? =A0We can just abort if expandin= g >>>> failed anyway. >>> >>> At first I thought your expansion idea was best, but now I think there = are valid scenarios where it fails. >>> >>> Imagine both sides are not using a file but a disk partition as storage= . If the partition size is not rounded to 1 MB, the last write will fail wi= th the current code, and there is no way we can expand the partition. >>> >> >> Right. =A0But in case of partition doesn't the check in the patch below >> return error? =A0Does bdrv_getlength return the size correctly? > > I'm pretty sure that it does. We would have problems in other places if > it didn't (e.g. we're checking if I/O requests are within the disk size). Sorry for the noise. I just learned it's returning the value of lseek in case of raw-posix. Yoshi > > Kevin > >