[libvirt] [PATCH 1/6] util: file: introduce VIR_AUTOCLOSE macro to close fd of the file automatically

[Shi Lei]

On 2018-09-12 at 15:18, Erik Skultety wrote:
>On Tue, Sep 11, 2018 at 10:31:18PM +0800, Shi Lei wrote:
>> On 2018-09-11 at 20:22, Michal Privoznik wrote:
>> >On 09/10/2018 05:47 AM, Shi Lei wrote:
>> >> By making use of GNU C's cleanup attribute handled by the VIR_AUTOCLOSE macro,
>> >> many of the VIR_FORCE_CLOSE calls can be dropped, which in turn leads to
>> >> getting rid of many of our cleanup sections.
>> >>
>> >> Signed-off-by: Shi Lei <shi_lei at massclouds.com>
>> >> ---
>> >>  src/util/virfile.h | 20 ++++++++++++++++++--
>> >>  1 file changed, 18 insertions(+), 2 deletions(-)
>> >>
>> >> diff --git a/src/util/virfile.h b/src/util/virfile.h
>> >> index b30a1d3..70e7203 100644
>> >> --- a/src/util/virfile.h
>> >> +++ b/src/util/virfile.h
>> >> @@ -54,6 +54,11 @@ int virFileClose(int *fdptr, virFileCloseFlags flags)
>> >>  int virFileFclose(FILE **file, bool preserve_errno) ATTRIBUTE_RETURN_CHECK;
>> >>  FILE *virFileFdopen(int *fdptr, const char *mode) ATTRIBUTE_RETURN_CHECK;
>> >>
>> >> +static inline void virForceCloseHelper(int *_fd)
>> >
>> >No need for this argument to have underscore in its name.
>>
>> Okay.
>>
>> >
>> >> +{
>> >> +    ignore_value(virFileClose(_fd, VIR_FILE_CLOSE_PRESERVE_ERRNO));
>> >> +}
>> >> +
>> >>  /* For use on normal paths; caller must check return value,
>> >>     and failure sets errno per close. */
>> >>  # define VIR_CLOSE(FD) virFileClose(&(FD), 0)
>> >> @@ -64,8 +69,7 @@ FILE *virFileFdopen(int *fdptr, const char *mode) ATTRIBUTE_RETURN_CHECK;
>> >>
>> >>  /* For use on cleanup paths; errno is unaffected by close,
>> >>     and no return value to worry about. */
>> >> -# define VIR_FORCE_CLOSE(FD) \
>> >> -    ignore_value(virFileClose(&(FD), VIR_FILE_CLOSE_PRESERVE_ERRNO))
>> >> +# define VIR_FORCE_CLOSE(FD) virForceCloseHelper(&(FD))
>> >>  # define VIR_FORCE_FCLOSE(FILE) ignore_value(virFileFclose(&(FILE), true))
>> >>
>> >>  /* Similar VIR_FORCE_CLOSE() but ignores EBADF errors since they are expected
>> >> @@ -80,6 +84,18 @@ FILE *virFileFdopen(int *fdptr, const char *mode) ATTRIBUTE_RETURN_CHECK;
>> >>                   VIR_FILE_CLOSE_PRESERVE_ERRNO | \
>> >>                   VIR_FILE_CLOSE_DONT_LOG))
>> >>
>> >> +/**
>> >> + * VIR_AUTOCLOSE:
>> >> + * @fd: fd of the file to be closed automatically
>> >> + *
>> >> + * Macro to automatically force close the fd by calling virForceCloseHelper
>> >> + * when the fd goes out of scope. It's used to eliminate VIR_FORCE_CLOSE
>> >> + * in cleanup sections.
>> >> + */
>> >> +# define VIR_AUTOCLOSE(fd) \
>> >> +    __attribute__((cleanup(virForceCloseHelper))) int fd = -1
>> >
>> >While this may helps us to initialize variables correctly, I think we
>> >should do that explicitly. Not only it follows what VIR_AUTOFREE is
>> >doing, it also is more visible when used. For instance, in 2/6 when the
>> >macro is used for the first time, it's not visible what is @fd
>> >initialized to.
>>
>> Okay. So I think the macro could be like:
>>
>> # define VIR_AUTOCLOSE \
>>    __attribute__((cleanup(virForceCloseHelper))) int
>
>Actually, I'd prefer if we stayed consistent with the existing AUTO_ macros,
>IOW, the form of VIR_AUTOCLOSE(fd) = <rvalue> is IMHO desired. 

Okay. Then the syntax-check rule would be simpler.

>
>>
>> And the statement is like:
>>
>> VIR_AUTOCLOSE fd = -1;
>> VIR_AUTOCLOSE sock_fd = socket(VIR_NETDEV_FAMILY, SOCK_DGRAM, 0);
>>
>> Also, I think I should add a new syntax-check rule to ensure the initialization
>> of the variable. Just like sc_require_attribute_cleanup_initialization
>> for VIR_AUTO(FREE|PTR).
>
>Yep, I agree with adding a similar syntax-check rule.
>
>Erik 

Okay. Just now, I find that we do not need to add a new rule. A minor change on
sc_require_attribute_cleanup_initialization can work.

Shi Lei