* [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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