From 6f1953c4c14566d3303709869fd26201828b3ccf Mon Sep 17 00:00:00 2001 From: Christoph Hellwig Date: Fri, 4 Sep 2009 19:01:32 +0200 Subject: block: use fdatasync instead of fsync if possible If we are flushing the caches for our image files we only care about the data (including the metadata required for accessing it) but not things like timestamp updates. So try to use fdatasync instead of fsync to implement the flush operations. Unfortunately many operating systems still do not support fdatasync, so we add a qemu_fdatasync wrapper that uses fdatasync if available as per the _POSIX_SYNCHRONIZED_IO feature macro or fsync otherwise. Signed-off-by: Christoph Hellwig Signed-off-by: Anthony Liguori --- cutils.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) (limited to 'cutils.c') diff --git a/cutils.c b/cutils.c index ffe5c71..7a22346 100644 --- a/cutils.c +++ b/cutils.c @@ -115,6 +115,22 @@ int qemu_fls(int i) return 32 - clz32(i); } +/* + * Make sure data goes on disk, but if possible do not bother to + * write out the inode just for timestamp updates. + * + * Unfortunately even in 2009 many operating systems do not support + * fdatasync and have to fall back to fsync. + */ +int qemu_fdatasync(int fd) +{ +#ifdef _POSIX_SYNCHRONIZED_IO + return fdatasync(fd); +#else + return fsync(fd); +#endif +} + /* io vectors */ void qemu_iovec_init(QEMUIOVector *qiov, int alloc_hint) -- cgit v1.1