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| author | Nir Soffer <nirsof@gmail.com> | 2017-02-17 02:51:27 +0200 |
|---|---|---|
| committer | Kevin Wolf <kwolf@redhat.com> | 2017-02-24 16:09:23 +0100 |
| commit | c6ccc2c5e6a58a847f51075abfef20e212c1a3e5 (patch) | |
| tree | de31e895999cfacd8fee6aba614fb28af93e3330 /block/file-posix.c | |
| parent | 5a1dad9d5a5777c4883de78d9f35bd8141175798 (diff) | |
| download | qemu-c6ccc2c5e6a58a847f51075abfef20e212c1a3e5.zip | |
qemu-img: Improve documentation for PREALLOC_MODE_FALLOC
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 <nirsof@gmail.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Diffstat (limited to 'block/file-posix.c')
| -rw-r--r-- | block/file-posix.c | 7 |
1 files changed, 6 insertions, 1 deletions
diff --git a/block/file-posix.c b/block/file-posix.c index d24e34be36..4de1abd023 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"); } |