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

[Erik Skultety]

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.

>
> 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