Fam Zheng <f...@redhat.com> writes: > 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()?
If you know ERRP can't be null, then error_is_set(ERRP) is pointless. Just test *ERRP instead. If ERRP may be null, then error_is_set(ERRP) makes some sense: it saves you spelling out ERRP && *ERRP. Personally, I'd prefer it spelled out, though. Note that testing an Error ** that may be null to answer the question "did this fail" is *wrong*, regardless of whether you use error_is_set() or spell it out.