On Sun, Mar 22, 2015 at 3:38 PM, Michael Kerrisk (man-pages) <mtk.manpages@xxxxxxxxx> wrote: > Hello all, > > I wrote a short man page documented some of the details of > NPTL that might affect application developers. Review comments > would be most welcome. > > Thanks, > > Michael > > === > .\" Copyright (c) 2015 by Michael Kerrisk <mtk.manpages@xxxxxxxxx> > .\" > .\" %%%LICENSE_START(VERBATIM) > .\" Permission is granted to make and distribute verbatim copies of this > .\" manual provided the copyright notice and this permission notice are > .\" preserved on all copies. > .\" > .\" Permission is granted to copy and distribute modified versions of this > .\" manual under the conditions for verbatim copying, provided that the > .\" entire resulting derived work is distributed under the terms of a > .\" permission notice identical to this one. > .\" > .\" Since the Linux kernel and libraries are constantly changing, this > .\" manual page may be incorrect or out-of-date. The author(s) assume no > .\" responsibility for errors or omissions, or for damages resulting from > .\" the use of the information contained herein. The author(s) may not > .\" have taken the same level of care in the production of this manual, > .\" which is licensed free of charge, as they might when working > .\" professionally. > .\" > .\" Formatted or processed versions of this manual, if unaccompanied by > .\" the source, must acknowledge the copyright and authors of this work. > .\" %%%LICENSE_END > .\" > .\" > .TH NPTL 7 2015-03-21 "Linux" "Linux Programmer's Manual" > .SH NAME > nptl \- Native POSIX Threads Library > .SH DESCRIPTION > NPTL (Native POSIX Threads Library) > is the GNU C library POSIX threads implementation that is used on modern > Linux systems. > .\" > .SS NPTL and signals > NPTL makes internal use of the first two real-time signals > (signal numbers 32 and 33). > One of these signals is used to support thread cancellation and POSIX timers; > the other is used as part of a mechanism that ensures all threads in > a process always have the same UIDs and GIDs, as required by POSIX. > These signals cannot be used in applications. > > To prevent accidental use of these signals in applications, > which might interfere with the operation of the NPTL implementation, > various glibc library functions and system call wrapper functions > attempt to hide these signals from applications, > as follows: > .IP * 3 > .B SIGRTMIN > is defined with the value 34 (rather than 32). > .IP * > The > .BR sigwaitinfo (2), > .BR sigtimedwait (2), > and > .BR sigwait (3) > interfaces silently ignore requests to wait for these two signals > if they are specified in the signal set argument of these calls. > .IP * > The > .BR sigprocmask (2) > and > .BR pthread_sigmask (3) > interfaces silently ignore attempts to block these two signals. > .IP * > The > .BR sigaction (2), > .BR pthread_kill (3), > and > .BR pthread_sigqueue (3) > interfaces fail with the error > .B EINVAL > (indicating an invalid signal number) if these signals are specified. > .IP * > .BR sigfillset (3) > does not include these two signals when it creates a full signal set. > .\" > .SS NPTL and process credential changes > At the Linux kernel level, > credentials (user and group IDs) are a per-thread attribute. > However, POSIX requires that all of the POSIX threads in a process > have the same credentials. > To accommodate this requirement, > the NPTL implementation wraps all of the system calls that > change process credentials with functions that, > in addition to invoking the underlying system call, > arrange for all other threads in the process to also change their credentials. > > The implementation of each of these system calls involves the use of > a real-time signal that is sent (using > .BR tgkill (2)) > to each of the other threads that must change change its credentials. s/change change/change/ Bert > Before sending these signals, the thread that is changing credentials > saves the new credential(s) and records the system call being employed > in a global buffer. > A signal handler in the receiving thread(s) fetches this information and > then uses the same system call to change its credentials. > > Wrapper functions employing this technique are provided for > .BR setgid (2), > .BR setuid (2), > .BR setegid (2), > .BR seteuid (2), > .BR setregid (2), > .BR setreuid (2), > .BR setresgid (2), > .BR setresuid (2), > and > .BR setgroups (2). > .SH CONFORMING TO > For details of the conformance of NPTL to the POSIX standard, see > .BR pthreads (7). > .SH SEE ALSO > .BR credentials (7), > .BR pthreads (7), > .BR signal (7), > .BR standards (7) > > -- > Michael Kerrisk > Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ > Linux/UNIX System Programming Training: http://man7.org/training/ > -- > To unsubscribe from this list: send the line "unsubscribe linux-man" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
