Am 17.02.2014 um 14:15 hat Fam Zheng geschrieben: > On Sat, 02/15 11:01, Markus Armbruster wrote: > > Jeff Cody <jc...@redhat.com> writes: > > > > > On Fri, Feb 14, 2014 at 05:45:40PM +0100, Kevin Wolf wrote: > > >> Am 11.02.2014 um 18:03 hat Paolo Bonzini geschrieben: > > >> > Signed-off-by: Paolo Bonzini <pbonz...@redhat.com> > > >> > --- > > >> > block/cow.c | 12 +++--------- > > >> > 1 file changed, 3 insertions(+), 9 deletions(-) > > >> > > > >> > diff --git a/block/cow.c b/block/cow.c > > >> > index 7fc0b12..43a2150 100644 > > >> > --- a/block/cow.c > > >> > +++ b/block/cow.c > > >> > @@ -82,7 +82,7 @@ static int cow_open(BlockDriverState *bs, QDict > > >> > *options, int flags, > > >> > char version[64]; > > >> > snprintf(version, sizeof(version), > > >> > "COW version %d", cow_header.version); > > >> > - qerror_report(QERR_UNKNOWN_BLOCK_FORMAT_FEATURE, > > >> > + error_set(errp, QERR_UNKNOWN_BLOCK_FORMAT_FEATURE, > > >> > bs->device_name, "cow", version); > > >> > ret = -ENOTSUP; > > >> > goto fail; > > >> > @@ -330,7 +330,6 @@ static int cow_create(const char *filename, > > >> > QEMUOptionParameter *options, > > >> > struct stat st; > > >> > int64_t image_sectors = 0; > > >> > const char *image_filename = NULL; > > >> > - Error *local_err = NULL; > > >> > int ret; > > >> > BlockDriverState *cow_bs; > > >> > > > >> > @@ -344,18 +343,13 @@ static int cow_create(const char *filename, > > >> > QEMUOptionParameter *options, > > >> > options++; > > >> > } > > >> > > > >> > - ret = bdrv_create_file(filename, options, &local_err); > > >> > + ret = bdrv_create_file(filename, options, errp); > > >> > if (ret < 0) { > > >> > - qerror_report_err(local_err); > > >> > - error_free(local_err); > > >> > return ret; > > >> > } > > >> > > > >> > - ret = bdrv_file_open(&cow_bs, filename, NULL, NULL, BDRV_O_RDWR, > > >> > - &local_err); > > >> > + ret = bdrv_file_open(&cow_bs, filename, NULL, NULL, BDRV_O_RDWR, > > >> > errp); > > >> > if (ret < 0) { > > >> > - qerror_report_err(local_err); > > >> > - error_free(local_err); > > >> > return ret; > > >> > } > > >> > > >> This is technically correct, but I think general policy is that using > > >> the local_err pattern is preferred anyway. > > >> > > > > > > If I recall correct, I think there are several places that pass errp > > > along. How about this for a rule of thumb policy: use the local_err > > > method if the function does not indicate error outside of the passed > > > Error pointer. > > > > Use &local_err when you need to examine the error object. Passing errp > > directly is no good then, because it may be null. > > > > When you're forwarding errors without examining them, then passing errp > > directly is just fine. > > > > Does this mean that error_is_set() is always used by programmer to check a > non-NULL error pointer? Is there any case to call error_is_set(errp) without > knowing if errp is NULL or not? If no, should we enforce the rule and add > assert(errp) in error_is_set()?
Sounds like a good idea to me, it would catch bugs where you forget to use a local_err. Of course, it requires that error_is_set() is used instead of just using errp as a boolean, but such an assertion could actually be a reason to make this the policy. Kevin