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* [musl] [PATCH] remove extraneous syscall from fopen(3)
@ 2022-08-15 17:50 Érico Nogueira
  2022-08-15 17:54 ` Rich Felker
  0 siblings, 1 reply; 8+ messages in thread
From: Érico Nogueira @ 2022-08-15 17:50 UTC (permalink / raw)
  To: musl; +Cc: Érico Nogueira

the __fdopen() call afterwards will set the close-on-exec flag with the
same syscall if "e" was specified in mode
---
 src/stdio/fopen.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/src/stdio/fopen.c b/src/stdio/fopen.c
index e1b91e12..22b72edf 100644
--- a/src/stdio/fopen.c
+++ b/src/stdio/fopen.c
@@ -20,8 +20,6 @@ FILE *fopen(const char *restrict filename, const char *restrict mode)
 
 	fd = sys_open(filename, flags, 0666);
 	if (fd < 0) return 0;
-	if (flags & O_CLOEXEC)
-		__syscall(SYS_fcntl, fd, F_SETFD, FD_CLOEXEC);
 
 	f = __fdopen(fd, mode);
 	if (f) return f;
-- 
2.37.2


^ permalink raw reply	[flat|nested] 8+ messages in thread

* Re: [musl] [PATCH] remove extraneous syscall from fopen(3)
  2022-08-15 17:50 [musl] [PATCH] remove extraneous syscall from fopen(3) Érico Nogueira
@ 2022-08-15 17:54 ` Rich Felker
  2022-08-15 17:58   ` Érico Nogueira
  0 siblings, 1 reply; 8+ messages in thread
From: Rich Felker @ 2022-08-15 17:54 UTC (permalink / raw)
  To: Érico Nogueira; +Cc: musl

On Mon, Aug 15, 2022 at 02:50:21PM -0300, Érico Nogueira wrote:
> the __fdopen() call afterwards will set the close-on-exec flag with the
> same syscall if "e" was specified in mode
> ---
>  src/stdio/fopen.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/src/stdio/fopen.c b/src/stdio/fopen.c
> index e1b91e12..22b72edf 100644
> --- a/src/stdio/fopen.c
> +++ b/src/stdio/fopen.c
> @@ -20,8 +20,6 @@ FILE *fopen(const char *restrict filename, const char *restrict mode)
>  
>  	fd = sys_open(filename, flags, 0666);
>  	if (fd < 0) return 0;
> -	if (flags & O_CLOEXEC)
> -		__syscall(SYS_fcntl, fd, F_SETFD, FD_CLOEXEC);
>  
>  	f = __fdopen(fd, mode);
>  	if (f) return f;
> -- 
> 2.37.2

See commit 7765706c0584ed4a30e0b7a3ada742e490ef02b0

^ permalink raw reply	[flat|nested] 8+ messages in thread

* Re: [musl] [PATCH] remove extraneous syscall from fopen(3)
  2022-08-15 17:54 ` Rich Felker
@ 2022-08-15 17:58   ` Érico Nogueira
  2022-08-15 18:16     ` Rich Felker
  0 siblings, 1 reply; 8+ messages in thread
From: Érico Nogueira @ 2022-08-15 17:58 UTC (permalink / raw)
  To: Rich Felker; +Cc: musl

On Mon Aug 15, 2022 at 2:54 PM -03, Rich Felker wrote:
> On Mon, Aug 15, 2022 at 02:50:21PM -0300, Érico Nogueira wrote:
> > the __fdopen() call afterwards will set the close-on-exec flag with the
> > same syscall if "e" was specified in mode
> > ---
> >  src/stdio/fopen.c | 2 --
> >  1 file changed, 2 deletions(-)
> > 
> > diff --git a/src/stdio/fopen.c b/src/stdio/fopen.c
> > index e1b91e12..22b72edf 100644
> > --- a/src/stdio/fopen.c
> > +++ b/src/stdio/fopen.c
> > @@ -20,8 +20,6 @@ FILE *fopen(const char *restrict filename, const char *restrict mode)
> >  
> >  	fd = sys_open(filename, flags, 0666);
> >  	if (fd < 0) return 0;
> > -	if (flags & O_CLOEXEC)
> > -		__syscall(SYS_fcntl, fd, F_SETFD, FD_CLOEXEC);
> >  
> >  	f = __fdopen(fd, mode);
> >  	if (f) return f;
> > -- 
> > 2.37.2
>
> See commit 7765706c0584ed4a30e0b7a3ada742e490ef02b0

If the relevant part of that commit is that the flag is added
immediately after, would moving the SYS_fcntl call in __fdopen to the
top of the functon be acceptable?

^ permalink raw reply	[flat|nested] 8+ messages in thread

* Re: [musl] [PATCH] remove extraneous syscall from fopen(3)
  2022-08-15 17:58   ` Érico Nogueira
@ 2022-08-15 18:16     ` Rich Felker
  2022-08-15 18:31       ` Érico Nogueira
  2022-08-20  8:49       ` Szabolcs Nagy
  0 siblings, 2 replies; 8+ messages in thread
From: Rich Felker @ 2022-08-15 18:16 UTC (permalink / raw)
  To: Érico Nogueira; +Cc: musl

On Mon, Aug 15, 2022 at 02:58:40PM -0300, Érico Nogueira wrote:
> On Mon Aug 15, 2022 at 2:54 PM -03, Rich Felker wrote:
> > On Mon, Aug 15, 2022 at 02:50:21PM -0300, Érico Nogueira wrote:
> > > the __fdopen() call afterwards will set the close-on-exec flag with the
> > > same syscall if "e" was specified in mode
> > > ---
> > >  src/stdio/fopen.c | 2 --
> > >  1 file changed, 2 deletions(-)
> > > 
> > > diff --git a/src/stdio/fopen.c b/src/stdio/fopen.c
> > > index e1b91e12..22b72edf 100644
> > > --- a/src/stdio/fopen.c
> > > +++ b/src/stdio/fopen.c
> > > @@ -20,8 +20,6 @@ FILE *fopen(const char *restrict filename, const char *restrict mode)
> > >  
> > >  	fd = sys_open(filename, flags, 0666);
> > >  	if (fd < 0) return 0;
> > > -	if (flags & O_CLOEXEC)
> > > -		__syscall(SYS_fcntl, fd, F_SETFD, FD_CLOEXEC);
> > >  
> > >  	f = __fdopen(fd, mode);
> > >  	if (f) return f;
> > > -- 
> > > 2.37.2
> >
> > See commit 7765706c0584ed4a30e0b7a3ada742e490ef02b0
> 
> If the relevant part of that commit is that the flag is added
> immediately after, would moving the SYS_fcntl call in __fdopen to the
> top of the functon be acceptable?

Oh, I missed that it also happens in __fdopen from the 'e' being
present, and misunderstood your patch as just removing the fallback
entirely.

No, it's not acceptable to move the fcntl in __fdopen above the malloc
because it would make fdopen modify the fd status on failure. I guess
it's questionable whether we care "how soon" after the open it happens
-- either way this is not a thread-safe fallback precluding fd leak on
old/broken kernels. But since malloc may be application-provided,
failure to set it before the malloc like we're doing now would be a
"worse behavior" in some sense, exposing the incorrect fd state to a
non-multithreaded application. So I'm not sure if it's a good idea to
change this or not. Do you have reason to believe it's affecting
performance in real-world usage?

Rich

^ permalink raw reply	[flat|nested] 8+ messages in thread

* Re: [musl] [PATCH] remove extraneous syscall from fopen(3)
  2022-08-15 18:16     ` Rich Felker
@ 2022-08-15 18:31       ` Érico Nogueira
  2022-08-15 18:57         ` Rich Felker
  2022-08-20  8:49       ` Szabolcs Nagy
  1 sibling, 1 reply; 8+ messages in thread
From: Érico Nogueira @ 2022-08-15 18:31 UTC (permalink / raw)
  To: musl

On Mon Aug 15, 2022 at 3:16 PM -03, Rich Felker wrote:
> On Mon, Aug 15, 2022 at 02:58:40PM -0300, Érico Nogueira wrote:
> > On Mon Aug 15, 2022 at 2:54 PM -03, Rich Felker wrote:
> > > On Mon, Aug 15, 2022 at 02:50:21PM -0300, Érico Nogueira wrote:
> > > > the __fdopen() call afterwards will set the close-on-exec flag with the
> > > > same syscall if "e" was specified in mode
> > > > ---
> > > >  src/stdio/fopen.c | 2 --
> > > >  1 file changed, 2 deletions(-)
> > > > 
> > > > diff --git a/src/stdio/fopen.c b/src/stdio/fopen.c
> > > > index e1b91e12..22b72edf 100644
> > > > --- a/src/stdio/fopen.c
> > > > +++ b/src/stdio/fopen.c
> > > > @@ -20,8 +20,6 @@ FILE *fopen(const char *restrict filename, const char *restrict mode)
> > > >  
> > > >  	fd = sys_open(filename, flags, 0666);
> > > >  	if (fd < 0) return 0;
> > > > -	if (flags & O_CLOEXEC)
> > > > -		__syscall(SYS_fcntl, fd, F_SETFD, FD_CLOEXEC);
> > > >  
> > > >  	f = __fdopen(fd, mode);
> > > >  	if (f) return f;
> > > > -- 
> > > > 2.37.2
> > >
> > > See commit 7765706c0584ed4a30e0b7a3ada742e490ef02b0
> > 
> > If the relevant part of that commit is that the flag is added
> > immediately after, would moving the SYS_fcntl call in __fdopen to the
> > top of the functon be acceptable?
>
> Oh, I missed that it also happens in __fdopen from the 'e' being
> present, and misunderstood your patch as just removing the fallback
> entirely.
>
> No, it's not acceptable to move the fcntl in __fdopen above the malloc
> because it would make fdopen modify the fd status on failure. I guess
> it's questionable whether we care "how soon" after the open it happens
> -- either way this is not a thread-safe fallback precluding fd leak on
> old/broken kernels. But since malloc may be application-provided,
> failure to set it before the malloc like we're doing now would be a
> "worse behavior" in some sense, exposing the incorrect fd state to a
> non-multithreaded application.

On some level, unless someone inherited a file descriptor or something
similar, I'd expect them to have used O_CLOEXEC if they are also using
"e" in mode. So hopefully this is not as much of a concern.

And I don't think fdopen setting the close-on-exec flag is behavior
users can rely on, seeing as glibc doesn't take "e" into account in
their fdopen implementation.

> So I'm not sure if it's a good idea to
> change this or not. Do you have reason to believe it's affecting
> performance in real-world usage?

From what testing I have done, a fcntl() call is essentially free, at
least when compared to the cost of open(). This commit was intended only
as cleanup.

>
> Rich


^ permalink raw reply	[flat|nested] 8+ messages in thread

* Re: [musl] [PATCH] remove extraneous syscall from fopen(3)
  2022-08-15 18:31       ` Érico Nogueira
@ 2022-08-15 18:57         ` Rich Felker
  0 siblings, 0 replies; 8+ messages in thread
From: Rich Felker @ 2022-08-15 18:57 UTC (permalink / raw)
  To: Érico Nogueira; +Cc: musl

On Mon, Aug 15, 2022 at 03:31:30PM -0300, Érico Nogueira wrote:
> On Mon Aug 15, 2022 at 3:16 PM -03, Rich Felker wrote:
> > On Mon, Aug 15, 2022 at 02:58:40PM -0300, Érico Nogueira wrote:
> > > On Mon Aug 15, 2022 at 2:54 PM -03, Rich Felker wrote:
> > > > On Mon, Aug 15, 2022 at 02:50:21PM -0300, Érico Nogueira wrote:
> > > > > the __fdopen() call afterwards will set the close-on-exec flag with the
> > > > > same syscall if "e" was specified in mode
> > > > > ---
> > > > >  src/stdio/fopen.c | 2 --
> > > > >  1 file changed, 2 deletions(-)
> > > > > 
> > > > > diff --git a/src/stdio/fopen.c b/src/stdio/fopen.c
> > > > > index e1b91e12..22b72edf 100644
> > > > > --- a/src/stdio/fopen.c
> > > > > +++ b/src/stdio/fopen.c
> > > > > @@ -20,8 +20,6 @@ FILE *fopen(const char *restrict filename, const char *restrict mode)
> > > > >  
> > > > >  	fd = sys_open(filename, flags, 0666);
> > > > >  	if (fd < 0) return 0;
> > > > > -	if (flags & O_CLOEXEC)
> > > > > -		__syscall(SYS_fcntl, fd, F_SETFD, FD_CLOEXEC);
> > > > >  
> > > > >  	f = __fdopen(fd, mode);
> > > > >  	if (f) return f;
> > > > > -- 
> > > > > 2.37.2
> > > >
> > > > See commit 7765706c0584ed4a30e0b7a3ada742e490ef02b0
> > > 
> > > If the relevant part of that commit is that the flag is added
> > > immediately after, would moving the SYS_fcntl call in __fdopen to the
> > > top of the functon be acceptable?
> >
> > Oh, I missed that it also happens in __fdopen from the 'e' being
> > present, and misunderstood your patch as just removing the fallback
> > entirely.
> >
> > No, it's not acceptable to move the fcntl in __fdopen above the malloc
> > because it would make fdopen modify the fd status on failure. I guess
> > it's questionable whether we care "how soon" after the open it happens
> > -- either way this is not a thread-safe fallback precluding fd leak on
> > old/broken kernels. But since malloc may be application-provided,
> > failure to set it before the malloc like we're doing now would be a
> > "worse behavior" in some sense, exposing the incorrect fd state to a
> > non-multithreaded application.
> 
> On some level, unless someone inherited a file descriptor or something
> similar, I'd expect them to have used O_CLOEXEC if they are also using
> "e" in mode. So hopefully this is not as much of a concern.
> 
> And I don't think fdopen setting the close-on-exec flag is behavior
> users can rely on, seeing as glibc doesn't take "e" into account in
> their fdopen implementation.

Then they probably need to fix this, as the POSIX-future 'e' behavior
(see #1526 and earlier stuff too, I think) specifies that presence of
'e' causes fdopen to set the FD_CLOEXEC flag and absence causes fdopen
to leave it alone.

Rich

^ permalink raw reply	[flat|nested] 8+ messages in thread

* Re: [musl] [PATCH] remove extraneous syscall from fopen(3)
  2022-08-15 18:16     ` Rich Felker
  2022-08-15 18:31       ` Érico Nogueira
@ 2022-08-20  8:49       ` Szabolcs Nagy
  2022-08-20  8:52         ` Szabolcs Nagy
  1 sibling, 1 reply; 8+ messages in thread
From: Szabolcs Nagy @ 2022-08-20  8:49 UTC (permalink / raw)
  To: Rich Felker; +Cc: Érico Nogueira, musl

* Rich Felker <dalias@libc.org> [2022-08-15 14:16:09 -0400]:

> On Mon, Aug 15, 2022 at 02:58:40PM -0300, Érico Nogueira wrote:
> > On Mon Aug 15, 2022 at 2:54 PM -03, Rich Felker wrote:
> > > On Mon, Aug 15, 2022 at 02:50:21PM -0300, Érico Nogueira wrote:
> > > > the __fdopen() call afterwards will set the close-on-exec flag with the
> > > > same syscall if "e" was specified in mode
> > > > ---
> > > >  src/stdio/fopen.c | 2 --
> > > >  1 file changed, 2 deletions(-)
> > > > 
> > > > diff --git a/src/stdio/fopen.c b/src/stdio/fopen.c
> > > > index e1b91e12..22b72edf 100644
> > > > --- a/src/stdio/fopen.c
> > > > +++ b/src/stdio/fopen.c
> > > > @@ -20,8 +20,6 @@ FILE *fopen(const char *restrict filename, const char *restrict mode)
> > > >  
> > > >  	fd = sys_open(filename, flags, 0666);
> > > >  	if (fd < 0) return 0;
> > > > -	if (flags & O_CLOEXEC)
> > > > -		__syscall(SYS_fcntl, fd, F_SETFD, FD_CLOEXEC);
> > > >  
> > > >  	f = __fdopen(fd, mode);
> > > >  	if (f) return f;
> > > > -- 
> > > > 2.37.2
> > >
> > > See commit 7765706c0584ed4a30e0b7a3ada742e490ef02b0
> > 
> > If the relevant part of that commit is that the flag is added
> > immediately after, would moving the SYS_fcntl call in __fdopen to the
> > top of the functon be acceptable?
> 
> Oh, I missed that it also happens in __fdopen from the 'e' being
> present, and misunderstood your patch as just removing the fallback
> entirely.
> 
> No, it's not acceptable to move the fcntl in __fdopen above the malloc
> because it would make fdopen modify the fd status on failure. I guess

shouldn't fopen close fd on fdopen failure?


> it's questionable whether we care "how soon" after the open it happens
> -- either way this is not a thread-safe fallback precluding fd leak on
> old/broken kernels. But since malloc may be application-provided,
> failure to set it before the malloc like we're doing now would be a
> "worse behavior" in some sense, exposing the incorrect fd state to a
> non-multithreaded application. So I'm not sure if it's a good idea to
> change this or not. Do you have reason to believe it's affecting
> performance in real-world usage?
> 
> Rich

^ permalink raw reply	[flat|nested] 8+ messages in thread

* Re: [musl] [PATCH] remove extraneous syscall from fopen(3)
  2022-08-20  8:49       ` Szabolcs Nagy
@ 2022-08-20  8:52         ` Szabolcs Nagy
  0 siblings, 0 replies; 8+ messages in thread
From: Szabolcs Nagy @ 2022-08-20  8:52 UTC (permalink / raw)
  To: Rich Felker, Érico Nogueira, musl

* Szabolcs Nagy <nsz@port70.net> [2022-08-20 10:49:43 +0200]:
> shouldn't fopen close fd on fdopen failure?

ignore me, it already does that.

^ permalink raw reply	[flat|nested] 8+ messages in thread

end of thread, other threads:[~2022-08-20  8:53 UTC | newest]

Thread overview: 8+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2022-08-15 17:50 [musl] [PATCH] remove extraneous syscall from fopen(3) Érico Nogueira
2022-08-15 17:54 ` Rich Felker
2022-08-15 17:58   ` Érico Nogueira
2022-08-15 18:16     ` Rich Felker
2022-08-15 18:31       ` Érico Nogueira
2022-08-15 18:57         ` Rich Felker
2022-08-20  8:49       ` Szabolcs Nagy
2022-08-20  8:52         ` Szabolcs Nagy

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