From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:33165) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WhjQm-0005NL-4P for qemu-devel@nongnu.org; Tue, 06 May 2014 13:45:34 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1WhjQe-0006SS-Hn for qemu-devel@nongnu.org; Tue, 06 May 2014 13:45:27 -0400 Received: from mx1.redhat.com ([209.132.183.28]:61150) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WhjQe-0006Rv-AM for qemu-devel@nongnu.org; Tue, 06 May 2014 13:45:20 -0400 Received: from int-mx02.intmail.prod.int.phx2.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id s46HjGGc001015 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK) for ; Tue, 6 May 2014 13:45:17 -0400 Message-ID: <53691FA8.7060600@redhat.com> Date: Tue, 06 May 2014 19:45:12 +0200 From: Max Reitz MIME-Version: 1.0 References: <1399320099-32457-1-git-send-email-mreitz@redhat.com> <20140506114958.GE15810@stefanha-thinkpad.redhat.com> In-Reply-To: <20140506114958.GE15810@stefanha-thinkpad.redhat.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] block/raw-posix: Fall back to SEEK_HOLE/SEEK_DATA List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Stefan Hajnoczi Cc: Kevin Wolf , qemu-devel@nongnu.org On 06.05.2014 13:49, Stefan Hajnoczi wrote: > On Mon, May 05, 2014 at 10:01:39PM +0200, Max Reitz wrote: >> The current version of raw-posix always uses ioctl(FS_IOC_FIEMAP) if >> FIEMAP is available; lseek with SEEK_HOLE/SEEK_DATA are not even >> compiled in in this case. However, there may be implementations which >> support the latter but not the former (e.g., NFSv4.2). In this case, >> raw-posix should fall back to lseek with SEEK_HOLE/SEEK_DATA if FIEMAP >> does not work. >> >> Signed-off-by: Max Reitz >> --- >> As Linux does not yet implement NFSv4.2 (I don't even know whether the >> specification is complete), I have no way of testing whether this >> actually works for the proposed case. But as it doesn't break any of the >> existing test cases, it should be fine. >> --- >> block/raw-posix.c | 27 +++++++++++++++++++++------ >> 1 file changed, 21 insertions(+), 6 deletions(-) >> >> diff --git a/block/raw-posix.c b/block/raw-posix.c >> index 3ce026d..e523633 100644 >> --- a/block/raw-posix.c >> +++ b/block/raw-posix.c >> @@ -146,6 +146,9 @@ typedef struct BDRVRawState { >> bool has_discard:1; >> bool has_write_zeroes:1; >> bool discard_zeroes:1; >> +#if defined CONFIG_FIEMAP && defined SEEK_HOLE && defined SEEK_DATA >> + bool use_seek_hole_data; >> +#endif >> } BDRVRawState; >> >> typedef struct BDRVRawReopenState { >> @@ -1291,6 +1294,7 @@ static int64_t coroutine_fn raw_co_get_block_status(BlockDriverState *bs, >> int64_t sector_num, >> int nb_sectors, int *pnum) >> { >> + BDRVRawState *s = bs->opaque; >> off_t start, data, hole; >> int64_t ret; >> >> @@ -1303,22 +1307,31 @@ static int64_t coroutine_fn raw_co_get_block_status(BlockDriverState *bs, >> ret = BDRV_BLOCK_DATA | BDRV_BLOCK_OFFSET_VALID | start; >> >> #ifdef CONFIG_FIEMAP >> - >> - BDRVRawState *s = bs->opaque; >> struct { >> struct fiemap fm; >> struct fiemap_extent fe; >> } f; >> >> +#if defined SEEK_HOLE && defined SEEK_DATA >> + if (s->use_seek_hole_data) { >> + goto try_seek_hole_data; >> + } >> +#endif > This is becoming hard to read due to the ifdefs and their relationships. > > A minor simplification is to change the bool field: > #if defined CONFIG_FIEMAP > bool use_fiemap; > #endif > > ... > > #if defined CONFIG_FIEMAP > if (s->use_fiemap) { > ...try fiemap... > } > #endif /* CONFIG_FIEMAP */ > > use_fiemap is not dependent on SEEK_HOLE/SEEK_DATA. That reduces the > amount of ifdefs needed. > > A bigger cleanup is extracting the FIEMAP and SEEK_HOLE/SEEK_DATA > implementations into their own static functions. Then > raw_co_get_block_status() becomes simpler and doesn't need ifdefs: > > ret = try_fiemap(...); > if (ret < 0) { > ret = try_seekhole(...); > } > if (ret < 0) { > ...report every block allocated by default.... > } > > In other words, let normal C control flow describe the relationships > between these code paths. Use ifdef only to nop out try_fiemap() and > try_seekhole(). > > What do you think? Great idea! I thought about using normal if's or something, but didn't think of this. Max