From d6ad222673fa4db2d76b4fcd1b839c8dbdc5e6b0 Mon Sep 17 00:00:00 2001 Message-Id: From: Kevin Wolf Date: Tue, 29 Oct 2013 17:52:10 +0100 Subject: [PATCH] block: Avoid unecessary drv->bdrv_getlength() calls RH-Author: Kevin Wolf Message-id: <1383069130-24660-1-git-send-email-kwolf@redhat.com> Patchwork-id: 55098 O-Subject: [RHEL-6.5 qemu-kvm PATCH] block: Avoid unecessary drv->bdrv_getlength() calls Bugzilla: 1022548 RH-Acked-by: Fam Zheng RH-Acked-by: Max Reitz RH-Acked-by: Markus Armbruster Bugzilla: 1022548 Brew: https://brewweb.devel.redhat.com/taskinfo?taskID=6480905 The block layer generally keeps the size of an image cached in bs->total_sectors so that it doesn't have to perform expensive operations to get the size whenever it needs it. This doesn't work however when using a backend that can change its size without qemu being aware of it, i.e. passthrough of removable media like CD-ROMs or floppy disks. For this reason, the caching is disabled when a removable device is used. It is obvious that checking whether the _guest_ device has removable media isn't the right thing to do when we want to know whether the size of the host backend can change. To make things worse, non-top-level BlockDriverStates never have any device attached, which makes qemu assume they are removable, so drv->bdrv_getlength() is always called on the protocol layer. In the case of raw-posix, this causes unnecessary lseek() system calls, which turned out to be rather expensive. This patch completely changes the logic and disables bs->total_sectors caching only for certain block driver types, for which a size change is expected: host_cdrom and host_floppy on POSIX, host_device on win32; also the raw format in case it sits on top of one of these protocols, but in the common case the nested bdrv_getlength() call on the protocol driver will use the cache again and avoid an expensive drv->bdrv_getlength() call. Signed-off-by: Kevin Wolf Reviewed-by: Paolo Bonzini (cherry picked from commit b94a2610573cd9314f244207c8b04cb75e42d7f8) Conflicts: block/raw-win32.c block/raw_bsd.c Signed-off-by: Kevin Wolf --- block.c | 7 ++++--- block/raw-posix.c | 9 ++++++--- block/raw-win32.c | 5 ++++- block/raw.c | 1 + block_int.h | 3 +++ 5 files changed, 18 insertions(+), 7 deletions(-) Signed-off-by: Michal Novotny --- block.c | 7 ++++--- block/raw-posix.c | 9 ++++++--- block/raw-win32.c | 5 ++++- block/raw.c | 1 + block_int.h | 3 +++ 5 files changed, 18 insertions(+), 7 deletions(-) diff --git a/block.c b/block.c index d5cbfe7..4c57615 100644 --- a/block.c +++ b/block.c @@ -2390,9 +2390,10 @@ int64_t bdrv_getlength(BlockDriverState *bs) if (!drv) return -ENOMEDIUM; - if (bdrv_dev_has_removable_media(bs)) { - if (drv->bdrv_getlength) { - return drv->bdrv_getlength(bs); + if (drv->has_variable_length) { + int ret = refresh_total_sectors(bs, bs->total_sectors); + if (ret < 0) { + return ret; } } return bs->total_sectors * BDRV_SECTOR_SIZE; diff --git a/block/raw-posix.c b/block/raw-posix.c index 76149f8..bd19cad 100644 --- a/block/raw-posix.c +++ b/block/raw-posix.c @@ -1117,7 +1117,8 @@ static BlockDriver bdrv_host_floppy = { .bdrv_aio_flush = raw_aio_flush, .bdrv_truncate = raw_truncate, - .bdrv_getlength = raw_getlength, + .bdrv_getlength = raw_getlength, + .has_variable_length = true, .bdrv_get_allocated_file_size = raw_get_allocated_file_size, @@ -1216,7 +1217,8 @@ static BlockDriver bdrv_host_cdrom = { .bdrv_aio_flush = raw_aio_flush, .bdrv_truncate = raw_truncate, - .bdrv_getlength = raw_getlength, + .bdrv_getlength = raw_getlength, + .has_variable_length = true, .bdrv_get_allocated_file_size = raw_get_allocated_file_size, @@ -1338,7 +1340,8 @@ static BlockDriver bdrv_host_cdrom = { .bdrv_aio_flush = raw_aio_flush, .bdrv_truncate = raw_truncate, - .bdrv_getlength = raw_getlength, + .bdrv_getlength = raw_getlength, + .has_variable_length = true, .bdrv_get_allocated_file_size = raw_get_allocated_file_size, diff --git a/block/raw-win32.c b/block/raw-win32.c index 8002100..1f03077 100644 --- a/block/raw-win32.c +++ b/block/raw-win32.c @@ -413,7 +413,10 @@ static BlockDriver bdrv_host_device = { .bdrv_read = raw_read, .bdrv_write = raw_write, - .bdrv_getlength = raw_getlength, + + .bdrv_getlength = raw_getlength, + .has_variable_length = true, + .bdrv_get_allocated_file_size = raw_get_allocated_file_size, }; diff --git a/block/raw.c b/block/raw.c index 40279d0..b55074b 100644 --- a/block/raw.c +++ b/block/raw.c @@ -135,6 +135,7 @@ static BlockDriver bdrv_raw = { .bdrv_probe = raw_probe, .bdrv_getlength = raw_getlength, + .has_variable_length = true, .bdrv_truncate = raw_truncate, .bdrv_is_inserted = raw_is_inserted, diff --git a/block_int.h b/block_int.h index bea2a48..a6cb355 100644 --- a/block_int.h +++ b/block_int.h @@ -182,8 +182,11 @@ struct BlockDriver { const char *protocol_name; int (*bdrv_truncate)(BlockDriverState *bs, int64_t offset); + int64_t (*bdrv_getlength)(BlockDriverState *bs); + bool has_variable_length; int64_t (*bdrv_get_allocated_file_size)(BlockDriverState *bs); + int (*bdrv_write_compressed)(BlockDriverState *bs, int64_t sector_num, const uint8_t *buf, int nb_sectors); -- 1.7.11.7