* [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)
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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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