Sometimes it may be handy for the callback to report error, even
though our current callbacks are trivial. Let's report an error
only if callback returns a well known value, otherwise assume it
reported error message on its own.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
---
 src/util/virfile.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/src/util/virfile.c b/src/util/virfile.c
index f99e7f95e1..dd065a537c 100644
--- a/src/util/virfile.c
+++ b/src/util/virfile.c
@@ -499,6 +499,10 @@ int virFileUnlock(int fd G_GNUC_UNUSED,
  * @uid:@gid (pass -1 for current uid/gid) and written by
  * @rewrite callback.
  *
+ * A negative value returned by @rewrite callback is treated as
+ * error and if the value is different to -1 then it's the
+ * callback's responsibility to report error.
+ *
  * Returns: 0 on success,
  *         -1 otherwise (with error reported)
  */
@@ -512,6 +516,7 @@ virFileRewrite(const char *path,
     g_autofree char *newfile = NULL;
     int fd = -1;
     int ret = -1;
+    int rc;
 
     newfile = g_strdup_printf("%s.new", path);
 
@@ -524,9 +529,11 @@ virFileRewrite(const char *path,
         goto cleanup;
     }
 
-    if (rewrite(fd, opaque) < 0) {
-        virReportSystemError(errno, _("cannot write data to file '%s'"),
-                             newfile);
+    if ((rc = rewrite(fd, opaque)) < 0) {
+        if (rc == -1) {
+            virReportSystemError(errno, _("cannot write data to file '%s'"),
+                                 newfile);
+        }
         goto cleanup;
     }
 
-- 
2.34.1

On Thu, Feb 10, 2022 at 12:13:25PM +0100, Michal Privoznik wrote:
> Sometimes it may be handy for the callback to report error, even
> though our current callbacks are trivial. Let's report an error
> only if callback returns a well known value, otherwise assume it
> reported error message on its own.
> 
> Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
> ---
>  src/util/virfile.c | 13 ++++++++++---
>  1 file changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/src/util/virfile.c b/src/util/virfile.c
> index f99e7f95e1..dd065a537c 100644
> --- a/src/util/virfile.c
> +++ b/src/util/virfile.c
> @@ -499,6 +499,10 @@ int virFileUnlock(int fd G_GNUC_UNUSED,
>   * @uid:@gid (pass -1 for current uid/gid) and written by
>   * @rewrite callback.
>   *
> + * A negative value returned by @rewrite callback is treated as
> + * error and if the value is different to -1 then it's the
> + * callback's responsibility to report error.

I'd sugest just updating the existing caller to always report
an error, rather than having different semantics for -1 vs -2.


> @@ -524,9 +529,11 @@ virFileRewrite(const char *path,
>          goto cleanup;
>      }
>  
> -    if (rewrite(fd, opaque) < 0) {
> -        virReportSystemError(errno, _("cannot write data to file '%s'"),
> -                             newfile);

And simply get rid of this virReportSystemError call entirely

> +    if ((rc = rewrite(fd, opaque)) < 0) {
> +        if (rc == -1) {
> +            virReportSystemError(errno, _("cannot write data to file '%s'"),
> +                                 newfile);
> +        }
>          goto cleanup;
>      }
>  
> -- 
> 2.34.1
> 

Regards,
Daniel
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On 2/10/22 17:12, Daniel P. Berrangé wrote:
> On Thu, Feb 10, 2022 at 12:13:25PM +0100, Michal Privoznik wrote:
>> Sometimes it may be handy for the callback to report error, even
>> though our current callbacks are trivial. Let's report an error
>> only if callback returns a well known value, otherwise assume it
>> reported error message on its own.
>>
>> Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
>> ---
>>  src/util/virfile.c | 13 ++++++++++---
>>  1 file changed, 10 insertions(+), 3 deletions(-)
>>
>> diff --git a/src/util/virfile.c b/src/util/virfile.c
>> index f99e7f95e1..dd065a537c 100644
>> --- a/src/util/virfile.c
>> +++ b/src/util/virfile.c
>> @@ -499,6 +499,10 @@ int virFileUnlock(int fd G_GNUC_UNUSED,
>>   * @uid:@gid (pass -1 for current uid/gid) and written by
>>   * @rewrite callback.
>>   *
>> + * A negative value returned by @rewrite callback is treated as
>> + * error and if the value is different to -1 then it's the
>> + * callback's responsibility to report error.
> 
> I'd sugest just updating the existing caller to always report
> an error, rather than having different semantics for -1 vs -2.
> 
> 
>> @@ -524,9 +529,11 @@ virFileRewrite(const char *path,
>>          goto cleanup;
>>      }
>>  
>> -    if (rewrite(fd, opaque) < 0) {
>> -        virReportSystemError(errno, _("cannot write data to file '%s'"),
>> -                             newfile);
> 
> And simply get rid of this virReportSystemError call entirely


Fair enough, I wanted to not change the signature of the callback,
because the filename is not passed into it. But that's fairly trivial
change.

Michal