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emulate SOCK_CLOEXEC and SOCK_NONBLOCK for old (pre-2.6.27) kernels

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also update syslog to use SOCK_CLOEXEC rather than separate fcntl
step, to make it safe in multithreaded programs that run external
programs.

emulation is not atomic; it could be made atomic by holding a lock on
forking during the operation, but this seems like overkill. my goal is
not to achieve perfect behavior on old kernels (which have plenty of
other imperfect behavior already) but to avoid catastrophic breakage
in (1) syslog, which would give no output on old kernels with the
change to use SOCK_CLOEXEC, and (2) programs built on a new kernel
where configure scripts detected a working SOCK_CLOEXEC, which later
get run on older kernels (they may otherwise fail to work completely).
This commit is contained in:
Rich Felker 2012-09-29 17:36:27 -04:00
commit 79a5e73e51
2 changed files with 15 additions and 3 deletions
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3
src/misc/syslog.c
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@ -51,8 +51,7 @@ static void __openlog(const char *ident, int opt, int facility)
if (!(opt & LOG_NDELAY) || log_fd>=0) return;
log_fd = socket(AF_UNIX, SOCK_DGRAM, 0);
fcntl(log_fd, F_SETFD, FD_CLOEXEC);
log_fd = socket(AF_UNIX, SOCK_DGRAM|SOCK_CLOEXEC, 0);
}
void openlog(const char *ident, int opt, int facility)

15
src/network/socket.c
View file

@ -1,7 +1,20 @@
#include <sys/socket.h>
#include <fcntl.h>
#include <errno.h>
#include "syscall.h"
int socket(int domain, int type, int protocol)
{
return socketcall(socket, domain, type, protocol, 0, 0, 0);
int s = socketcall(socket, domain, type, protocol, 0, 0, 0);
if (s<0 && errno==EINVAL && (type&(SOCK_CLOEXEC|SOCK_NONBLOCK))) {
s = socketcall(socket, domain,
type & ~(SOCK_CLOEXEC|SOCK_NONBLOCK),
protocol, 0, 0, 0);
if (s < 0) return s;
if (type & SOCK_CLOEXEC)
fcntl(s, F_SETFD, FD_CLOEXEC);
if (type & SOCK_NONBLOCK)
fcntl(s, F_SETFL, fcntl(s, F_GETFL) | O_NONBLOCK);
}
return s;
}