sigaction.2

rtlinux-3.1源代码

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.ta 8n 16n 24n 32n 40n 48n 56n 64n 72n  
.TH "sigaction" "2" 
.SH "NAME" 
sigaction \(em RTLinux POSIX signal handling functions 
.SH "SYNOPSIS" 
.PP 
.nf 
.ta 8n 16n 24n 32n 40n 48n 56n 64n 72n 
#include <posix/signal.h> 
 
int \fBsigaction\fP(int \fBsignum\fR, const struct sigaction *\fBact\fR, struct sigaction *\fBoldact\fR); 
 
int  \fBsigprocmask\fP(int  \fBhow\fR,  const  sigset_t *\fBset\fR, sigset_t *\fBoldset\fR); 
.fi 
.SH "DESCRIPTION" 
.PP 
Signals interactions with pthreads is one of the less well defined and most 
contentious parts of POSIX. Many problems come from the interaction between 
process signals and thread signals. RTLinux V3.0 uses the concept of 
process signals to provide an interface to hard interrupt handlers. The 
signals RTL_SIGIRQMIN  to  RTL_SIGIRQMIN + NR_IRQS refer to global hardware 
interrupts, and installing signal handlers is the same as installing interrupt 
handlers. 
.PP 
RTLinux provides the POSIX \fBsigaction\fP function to install handlers for hardware interrupts and also to provide POSIX signaling (this is 
incomplete in V3.0).  
.PP 
\fBsignum\fR specifies the signal and can be any valid signal except \fBSIGKILL\fP and \fBSIGSTOP\fP. 
.PP 
If \fBact\fR is non-null, the new action for signal \fBsignum\fR is installed from \fBact\fR.  If \fBoldact\fR is non-null, the previous action is saved in \fBoldact\fR. 
.PP 
The \fBsigaction\fP structure is defined as 
.PP 
.nf 
.ta 8n 16n 24n 32n 40n 48n 56n 64n 72n 
\f(CW       struct sigaction{ 
void (*sa_handler)(int); 
sigset_t sa_mask; 
int sa_flags; 
void (*sa_restorer)(void); 
unsigned int sa_focus; 
}\fR 
.fi 
.PP 
The \fBsa_focus\fR field is an RTLinux-specific extension that 
is a bit map defining which processors on an SMP system can accept these 
interrupts. This is machine-specific and may only be used for hardware  
interrupts using the RTL_SIGIRQMIN+n, to catch hardware interrupt n. 
.PP 
\fBsa_handler\fR specifies the action to be associated with signum and may be \fBSIG_DFL\fP for the default action, \fBSIG_IGN\fP to ignore this signal, or a pointer to a signal handling function. 
.PP 
\fBsa_mask\fR  gives  a  mask of signals which should be blocked during execution of the signal handler.  In addition,  the signal which triggered the handler will be blocked, unless the \fBSA_NODEFER\fP or \fBSA_NOMASK\fP flags are used. In V3 and prior RTLinux 
these flags have no effect. Furthermore, when a signal handler for a hard 
interrupt is entered all interrupts are blocked by default. 
.PP 
\fBsa_flags\fR specifies a set of flags which modify the behaviour of the signal handling process.  In RTLinux V3.0 and earlier these 
flags are ignored. 
.PP 
The \fBsa_focus\fR element is used to direct a hardware 
interrupt to a particular set of processors in an SMP system.  
This element has no effiect on soft-interrupts, on processor-specific 
interrupts (e.g. local timers and IPIs), on uni-processor systems, or where the interrupt control logic does not support interrupt focus. 
.PP 
The \fBsigprocmask\fP call is used to change the list of 
currently blocked signals in a single threaded process.  
POSIX states that the sigprocmask call has undefined operation 
in a multi-threaded process.  
In RTLinux, if the pthreads-based scheduling module 
(\fBrtl_sched\fP) is loaded or otherwise activated, 
the RT process is multithreaded and sigprocmask behavior undefined, unless the ``\fIhow\fP'' variable is set to \fBSIG_DISABLE\fP or \fBSIG_ENABLE\fP.  These two flags are RTLinux extensions.  The behaviour of the call is dependent on the value of how, as follows. 
.PP 
.IP "\fBSIG_BLOCK\fP" 10 
The set of blocked signals is the union of the current set and the set argument. 
.IP "\fBSIG_UNBLOCK\fP" 10 
The signals in set are removed from the current set of blocked signals.  It is legal to attempt to unblock a  signal  which  is  not blocked. 
.IP "\fBSIG_SETMASK\fP" 10 
The  set  of  blocked  signals is set to the argument set. 
.IP "\fBSIG_DISABLE\fP" 10 
Turns on local processor interrupts. 
.IP "\fBSIG_ENABLE\fP" 10 
Turns on local processor interrupts. 
.PP 
Note that in RTLinux, as in POSIX,  not all signals can be masked or blocked. 
.PP 
If \fBoldset\fR is non-null, the previous value  of  the  signal mask is stored in \fBoldset\fR. 
.SH "RETURN VALUES" 
.PP 
\fBsigaction\fP, \fBsigprocmask\fP, \fBsigpending\fP and \fBsigsuspend\fP return 0 on success and -1 on error. 
.SH "ERRORS" 
.IP "EINVAL" 10 
An invalid signal was specified.  This will also be generated  if  an  attempt  is  made  to change the action for \fBSIGKILL\fP or  \fBSIGSTOP\fP,  which  cannot  be caught. 
.IP "EFAULT" 10 
\fBact\fR,\fBoldact\fR, \fBset\fR or \fBoldset\fR point to memory which is not a valid part of the process address space. 
.IP "EINTR" 10 
System call was interrupted. This cannot happen in RTLinux V3.0 or prior. 
.SH "NOTES" 
.PP 
It is not possible to block \fBSIGKILL\fP or  \fBSIGSTOP\fP  with  the \fBsigprocmask\fP  call.   Attempts  to  do  so will be silently ignored. RTLinux also adds an additional set of unmaskable and uncatchable signals. 
.PP 
According to POSIX, the behaviour of a  process  is  undefined after it ignores a \fBSIGFP\fPE, \fBSIGILL\fP, or \fBSIGSEGV\fP signal that was not generated by the \fBkill()\fP or the \fBraise()\fP  functions.  Integer division by zero has undefined result.  On some architectures  it  will  generate  a \fBSIGFPE\fP  signal.  (Also, dividing the most negative integer by -1 may generate \fBSIGFPE\fP.)  Ignoring this signal might lead to  an  endless loop. 
.PP 
\fBSIGCHLD\fP cannot happen in V3.0 RTLinux or prior, since there 
is no way to create child processes. 
.PP 
The POSIX spec only defines SA_NOCLDSTOP.   Use  of  other \fBsa_flags\fR is non-portable. 
.PP 
\fBsigaction\fP can be called with a  null  second  argument  to query  the  current signal handler. It can also be used to check whether a given signal  is  valid  for  the  current machine, by  calling it  with null second and third arguments. 
.SH "SEE ALSO" 
\fIUNIX spec sigaction (link to URL ../susv2/xsh/sigaction.html) \fR, \fIUNIX spec kill(2) (link to URL ../susv2/xsh/kill.html) \fR 
.PP 
\(co2001 FSMLabs Inc. 
.PP 
All rights reserved. 
...\" created by instant / docbook-to-man, Thu 26 Jul 2001, 11:20