From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:57200) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bFcVh-0004mG-Nq for qemu-devel@nongnu.org; Wed, 22 Jun 2016 03:23:43 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bFcVf-0005Ss-G2 for qemu-devel@nongnu.org; Wed, 22 Jun 2016 03:23:40 -0400 Date: Wed, 22 Jun 2016 15:23:28 +0800 From: Fam Zheng Message-ID: <20160622072328.GD22636@ad.usersys.redhat.com> References: <1464943756-14143-1-git-send-email-famz@redhat.com> <1464943756-14143-5-git-send-email-famz@redhat.com> <20160617113435.GF5431@noname.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160617113435.GF5431@noname.redhat.com> Subject: Re: [Qemu-devel] [PATCH v6 04/22] block: Introduce image file locking List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Kevin Wolf Cc: qemu-devel@nongnu.org, Max Reitz , Jeff Cody , Markus Armbruster , Eric Blake , qemu-block@nongnu.org, rjones@redhat.com, stefanha@redhat.com, pbonzini@redhat.com, John Snow , berrange@redhat.com, den@openvz.org On Fri, 06/17 13:34, Kevin Wolf wrote: > Am 03.06.2016 um 10:48 hat Fam Zheng geschrieben: > > Block drivers can implement this new operation .bdrv_lockf to actually lock the > > image in the protocol specific way. > > > > Signed-off-by: Fam Zheng > > --- > > block.c | 57 +++++++++++++++++++++++++++++++++++++++++++++++ > > include/block/block.h | 11 ++++++++- > > include/block/block_int.h | 5 +++++ > > 3 files changed, 72 insertions(+), 1 deletion(-) > > > > diff --git a/block.c b/block.c > > index 736432f..4c2a3ff 100644 > > --- a/block.c > > +++ b/block.c > > @@ -854,6 +854,50 @@ out: > > g_free(gen_node_name); > > } > > > > +BdrvLockfCmd bdrv_get_locking_cmd(int flags) > > +{ > > + if (flags & BDRV_O_NO_LOCK) { > > + return BDRV_LOCKF_UNLOCK; > > + } else if (flags & BDRV_O_SHARED_LOCK) { > > + return BDRV_LOCKF_SHARED; > > + } else if (flags & BDRV_O_RDWR) { > > + return BDRV_LOCKF_EXCLUSIVE; > > + } else { > > + return BDRV_LOCKF_SHARED; > > + } > > +} > > It feels a bit counterintuitive to use the very same operation for > "start of critical section, but don't actually lock" and "end of > critical section". > > Is there a specific reason why you chose this instead of separate > .bdrv_lock/bdrv_unlock callbacks? Because unlike open(2)/close(2), locking and unlocking are typically implemented with one parameterized operation (fcntl(2)) underneath, I followed that naturally. > > > +static int bdrv_lock_unlock_image_do(BlockDriverState *bs, BdrvLockfCmd cmd) > > +{ > > + int ret; > > + > > + if (bs->cur_lock == cmd) { > > + return 0; > > + } else if (!bs->drv) { > > + return -ENOMEDIUM; > > + } else if (!bs->drv->bdrv_lockf) { > > + return 0; > > + } > > + ret = bs->drv->bdrv_lockf(bs, cmd); > > + if (ret == -ENOTSUP) { > > + /* Handle it the same way as !bs->drv->bdrv_lockf */ > > + ret = 0; > > + } else if (ret == 0) { > > + bs->cur_lock = cmd; > > + } > > + return ret; > > +} > > Okay, so the callback is supposed to support going from exclusive to > shared and vice versa? Noted for the next patches. Yes. > > > +static int bdrv_lock_image(BlockDriverState *bs) > > +{ > > + return bdrv_lock_unlock_image_do(bs, bdrv_get_locking_cmd(bs->open_flags)); > > +} > > + > > +static int bdrv_unlock_image(BlockDriverState *bs) > > +{ > > + return bdrv_lock_unlock_image_do(bs, BDRV_LOCKF_UNLOCK); > > +} > > + > > static QemuOptsList bdrv_runtime_opts = { > > .name = "bdrv_common", > > .head = QTAILQ_HEAD_INITIALIZER(bdrv_runtime_opts.head), > > @@ -1003,6 +1047,14 @@ static int bdrv_open_common(BlockDriverState *bs, BdrvChild *file, > > goto free_and_fail; > > } > > > > + if (!(open_flags & (BDRV_O_NO_LOCK | BDRV_O_INACTIVE))) { > > + ret = bdrv_lock_image(bs); > > + if (ret) { > > + error_setg(errp, "Failed to lock image"); > > + goto free_and_fail; > > + } > > + } > > + > > ret = refresh_total_sectors(bs, bs->total_sectors); > > if (ret < 0) { > > error_setg_errno(errp, -ret, "Could not refresh total sector count"); > > @@ -2164,6 +2216,7 @@ static void bdrv_close(BlockDriverState *bs) > > if (bs->drv) { > > BdrvChild *child, *next; > > > > + bdrv_unlock_image(bs); > > bs->drv->bdrv_close(bs); > > bs->drv = NULL; > > > > @@ -3187,6 +3240,9 @@ void bdrv_invalidate_cache(BlockDriverState *bs, Error **errp) > > error_setg_errno(errp, -ret, "Could not refresh total sector count"); > > return; > > } > > + if (!(bs->open_flags & BDRV_O_NO_LOCK)) { > > + bdrv_lock_image(bs); > > + } > > } > > I think the if is unnecessary, bdrv_lock_image() already looks at > BDRV_O_NO_LOCK. I intentionally made enum BDRV_O_LOCK_* start from non-zero, so bdrv_lock_image will call drv->bdrv_lockf even for BDRV_O_NO_LOCK. In the case of lock-mode=off, I think we should skip that. > > > void bdrv_invalidate_cache_all(Error **errp) > > @@ -3229,6 +3285,7 @@ static int bdrv_inactivate_recurse(BlockDriverState *bs, > > } > > > > if (setting_flag) { > > + ret = bdrv_unlock_image(bs); > > bs->open_flags |= BDRV_O_INACTIVE; > > } > > return 0; > > Kevin Fam