From: Nir Soffer <nir...@gmail.com> Now that we are truncating the file in both PREALLOC_MODE_FULL and PREALLOC_MODE_OFF, not truncating in PREALLOC_MODE_FALLOC looks odd. Add a comment explaining why we do not truncate in this case.
Signed-off-by: Nir Soffer <nir...@gmail.com> Signed-off-by: Kevin Wolf <kw...@redhat.com> --- block/file-posix.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/block/file-posix.c b/block/file-posix.c index d24e34b..4de1abd 100644 --- a/block/file-posix.c +++ b/block/file-posix.c @@ -1594,9 +1594,14 @@ static int raw_create(const char *filename, QemuOpts *opts, Error **errp) switch (prealloc) { #ifdef CONFIG_POSIX_FALLOCATE case PREALLOC_MODE_FALLOC: - /* posix_fallocate() doesn't set errno. */ + /* + * Truncating before posix_fallocate() makes it about twice slower on + * file systems that do not support fallocate(), trying to check if a + * block is allocated before allocating it, so don't do that here. + */ result = -posix_fallocate(fd, 0, total_size); if (result != 0) { + /* posix_fallocate() doesn't set errno. */ error_setg_errno(errp, -result, "Could not preallocate data for the new file"); } -- 1.8.3.1