Re: [musl] [PATCH] add close_range() syscall wrapper

["Érico Nogueira" <ericonr@disroot.org>]

On Wed Aug 17, 2022 at 9:35 PM -03, Rich Felker wrote:
> On Wed, Aug 10, 2022 at 01:03:11PM +0000, Guilherme Janczak wrote:
> > close_range() is a syscall present in FreeBSD 8.0 and Linux 5.9. glibc
> > 2.34 added a wrapper.
> > ---
>
> The existence of this operation has been controversial, and it's
> arguable that it should be excluded by policy not to support UB (it's
> UB to close fds you don't own that might be used internally by the
> implementation) though I'm not sure it really helps since folks who
> want to use it will just make the syscall directly. We should probably
> at least consider it for inclusion.

I remember an idea to implement fallback logic, in case the syscall is
unavailable, had been mentioned. It would then avoid whatever fallback
code the application tried to implement, which might not be as relevant,
now that opendir() can be called in a forked child. And I don't know if
there's interest in implementing anything more complex at all.

>
>
> >  include/unistd.h        | 3 +++
> >  src/linux/close_range.c | 8 ++++++++
> >  2 files changed, 11 insertions(+)
> >  create mode 100644 src/linux/close_range.c
> > 
> > diff --git a/include/unistd.h b/include/unistd.h
> > index 80be3b26..e4b8cbb1 100644
> > --- a/include/unistd.h
> > +++ b/include/unistd.h
> > @@ -161,6 +161,9 @@ unsigned ualarm(unsigned, unsigned);
> >  #define L_INCR 1
> >  #define L_XTND 2
> >  int brk(void *);
> > +#define CLOSE_RANGE_UNSHARE 0x01
> > +#define CLOSE_RANGE_CLOEXEC 0x02
> > +int close_range(unsigned int, unsigned int, int);
> >  void *sbrk(intptr_t);
> >  pid_t vfork(void);
> >  int vhangup(void);
> > diff --git a/src/linux/close_range.c b/src/linux/close_range.c
> > new file mode 100644
> > index 00000000..4c5cd68c
> > --- /dev/null
> > +++ b/src/linux/close_range.c
> > @@ -0,0 +1,8 @@
> > +#define _GNU_SOURCE
>
> This should probably be _BSD_SOURCE if it's exposed under _BSD_SOURCE.
>
> > +#include <unistd.h>
> > +#include "syscall.h"
> > +
> > +int close_range(unsigned int first, unsigned int last, int flags)
> > +{
> > +	return syscall(SYS_close_range, first, last, (unsigned int)flags);
> > +}
> > -- 
> > 2.35.1
>
> Can you elaborate on what the cast to unsigned is for?
>
> Rich