'Re: [PATCH-V3] xserver: Optional backtrace handler'

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List: freedesktop-xorg-devel
Subject: Re: [PATCH-V3] xserver: Optional backtrace handler
From: Barry Scott <barry.scott () onelan ! co ! uk>
Date: 2011-09-29 10:20:25
Message-ID: 201109291120.25421.barry.scott () onelan ! co ! uk
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On Wednesday 28 September 2011 18:37:04 Jeremy Huddleston wrote:
> After some thought, I think it's a good idea to not wait for the handler to exit. \
> It may want to do some extra processing that it doesn't need the process hanging \
> around for.

> 
> You probably meant one of these to be backtrace_handler_stdin:
> > + close(backtrace_handler_stdout);
> > + close(backtrace_handler_stdout);

Opss... V4 will fix this

> 
> I'd like to see a followup to set BacktraceHandlerPath from xorg.conf

Can I leave that to someone else?

Barry

> 
> On Sep 28, 2011, at 3:09 AM, Barry Scott wrote:
> 
> > It is useful to be able to run an external program to analyse
> > a crashed server process. The server will run a user supplied
> > program in a subprocess of the server.
> > 
> > The subprocess is created when the server starts up so that all
> > resources needed to create the subprocess are available. It is not
> > always possible to start up a process from within a crashed server.
> > For example if the malloc heap is corrupt fork will not work.
> > 
> > If the server crashes a "crash" message is sent to the handler on
> > its stdin. The handler can then respond in whatever way it wishes.
> > If the handler wants the server to continue, return from
> > xorg_backtrace, it must write a line to its stdout.
> > 
> > When the server exits normally the handler is sent the "exit"
> > message just before the server exits.
> > 
> > Signed-off-by: Barry Scott <barry.scott@onelan.co.uk>
> > Reviewed-by: Simon Farnsworth <simon.farnsworth@onelan.co.uk>
> > ---
> > change from V2:
> > * restore trailing NL in main.c
> > * beef up comments to make it clea how loops are exited
> > when the child process dies
> > * Use _X_HIDDEN for new symbols that are not to be exported
> > 
> > change from V1:
> > 
> > * check for EAGAIN and EINTR on calls to read(), write() and waitpid()
> > * put -backtrace into lexical position in the command parser and usage
> > * fix coding style white space and condition ordering
> > * update man page with more details
> > * call xorg_cleanup_backtrace() from FatalError()
> > 
> > dix/main.c | 5 ++
> > include/os.h | 3 +
> > man/Xserver.man | 20 +++++++++
> > os/backtrace.c | 123 +++++++++++++++++++++++++++++++++++++++++++++++++++++-
> > os/log.c | 3 +
> > os/utils.c | 8 ++++
> > 6 files changed, 159 insertions(+), 3 deletions(-)
> > 
> > diff --git a/dix/main.c b/dix/main.c
> > index 16575ce..3326e78 100644
> > --- a/dix/main.c
> > +++ b/dix/main.c
> > @@ -147,6 +147,8 @@ int main(int argc, char *argv[], char *envp[])
> > 
> > ProcessCommandLine(argc, argv);
> > 
> > + xorg_init_backtrace();
> > +
> > alwaysCheckForInput[0] = 0;
> > alwaysCheckForInput[1] = 1;
> > while(1)
> > @@ -354,6 +356,9 @@ int main(int argc, char *argv[], char *envp[])
> > 	free(ConnectionInfo);
> > 	ConnectionInfo = NULL;
> > }
> > +
> > + xorg_cleanup_backtrace();
> > +
> > return 0;
> > }
> > 
> > diff --git a/include/os.h b/include/os.h
> > index a553f57..00336e5 100644
> > --- a/include/os.h
> > +++ b/include/os.h
> > @@ -541,6 +541,9 @@ extern _X_EXPORT void ErrorF(const char *f, ...) \
> > _X_ATTRIBUTE_PRINTF(1,2); extern _X_EXPORT void Error(const char *str);
> > extern _X_EXPORT void LogPrintMarkers(void);
> > 
> > +extern _X_HIDDEN void xorg_init_backtrace(void);
> > extern _X_EXPORT void xorg_backtrace(void);
> > +extern _X_HIDDEN void xorg_cleanup_backtrace(void);
> > +extern _X_HIDDEN const char *BacktraceHandlerPath;
> > 
> > #endif /* OS_H */
> > diff --git a/man/Xserver.man b/man/Xserver.man
> > index f743912..9def022 100644
> > --- a/man/Xserver.man
> > +++ b/man/Xserver.man
> > @@ -100,6 +100,9 @@ specifies a file which contains a collection of authorization \
> > records used to authenticate access. See also the \fIxdm\fP(1) and
> > \fIXsecurity\fP(__miscmansuffix__) manual pages.
> > .TP 8
> > +.B \-backtrace \fIbacktrace-handler-path\fP
> > +specifies the path to the optional backtrace handler program. See \fBBACKTRACE \
> > HANDLER\fP below. +.TP 8
> > .B \-br
> > sets the default root window to solid black instead of the standard root weave
> > pattern. This is the default unless -retro or -wr is specified.
> > @@ -530,6 +533,23 @@ the following font path:
> > /usr/share/fonts/default/ghostscript
> > .fi
> > 
> > +.SH BACKTRACE HANDLER
> > +
> > +The optional backtrace handler program will be run in a subprocess when
> > +the server starts. The handler is invoked with argv[1] set to the PID
> > +of the server.
> > +.PP
> > +The handler is expected to read a line from stdin that will tell the
> > +handler what has happened to the server.
> > +.PP
> > +When the server is about to exit normally "exit\\n" is sent to the handler.
> > +.PP
> > +If the server crashes "crash\n" is sent to the handler and the server will
> > +wait for a line to be written out on the handler's stdout. This causes
> > +the server to return from the xorg_backtrace function. Typically after calling
> > +xorg_backtrace additional error messages are logged and the server shuts down.
> > +If you do not want the server to continue then kill it.
> > +
> > .SH FILES
> > .TP 30
> > .I /etc/X\fBn\fP.hosts
> > diff --git a/os/backtrace.c b/os/backtrace.c
> > index 7ca6dab..f9114eb 100644
> > --- a/os/backtrace.c
> > +++ b/os/backtrace.c
> > @@ -28,6 +28,11 @@
> > #include "os.h"
> > #include "misc.h"
> > 
> > +#include <unistd.h>
> > +#include <errno.h>
> > +#include <sys/types.h>
> > +#include <sys/wait.h>
> > +
> > #ifdef HAVE_BACKTRACE
> > #ifndef _GNU_SOURCE
> > #define _GNU_SOURCE
> > @@ -35,7 +40,7 @@
> > #include <dlfcn.h>
> > #include <execinfo.h>
> > 
> > -void xorg_backtrace(void)
> > +void xorg_builtin_backtrace(void)
> > {
> > void *array[64];
> > const char *mod;
> > @@ -180,7 +185,7 @@ static int xorg_backtrace_pstack(void) {
> > 
> > # if defined(HAVE_PSTACK) || defined(HAVE_WALKCONTEXT)
> > 
> > -void xorg_backtrace(void) {
> > +void xorg_builtin_backtrace(void) {
> > 
> > ErrorF("\nBacktrace:\n");
> > 
> > @@ -207,7 +212,119 @@ void xorg_backtrace(void) {
> > # else
> > 
> > /* Default fallback if we can't find any way to get a backtrace */
> > -void xorg_backtrace(void) { return; }
> > +void xorg_builtin_backtrace(void) { return; }
> > 
> > # endif
> > #endif
> > +
> > +const char *BacktraceHandlerPath = NULL;
> > +
> > +static int backtrace_handler_stdin;
> > +static int backtrace_handler_stdout;
> > +static pid_t child_pid;
> > +
> > +static const char cmd_crash[] = "crash\n";
> > +static const char cmd_exit[] = "exit\n";
> > +
> > +static void report_init_error(const char *msg) {
> > + /* prevent any further use of the handler */
> > + BacktraceHandlerPath = NULL;
> > + FatalError("%s - errno %d", msg, errno);
> > +}
> > +
> > +void xorg_init_backtrace(void) {
> > + char pid_buffer[32];
> > + int pipe_fds[2];
> > + int child_stdin;
> > + int child_stdout;
> > +
> > + if (!BacktraceHandlerPath)
> > + return;
> > +
> > + if (pipe(pipe_fds) != 0)
> > + report_init_error("failed to create pipe");
> > + backtrace_handler_stdin = pipe_fds[1];
> > + child_stdin = pipe_fds[0];
> > +
> > + if (pipe(pipe_fds) != 0)
> > + report_init_error("failed to create pipe");
> > + backtrace_handler_stdout = pipe_fds[0];
> > + child_stdout = pipe_fds[1];
> > +
> > + /* server pid will be passed in argv[1] */
> > + snprintf( pid_buffer, sizeof(pid_buffer), "%d", getpid());
> > +
> > + child_pid = fork();
> > + if (child_pid < 0) {
> > + report_init_error("failed to fork");
> > + } else {
> > + if (child_pid == 0) {
> > + /* setup stdin, stdout to point to the pipes */
> > + dup2(child_stdin, STDIN_FILENO);
> > + dup2(child_stdout, STDOUT_FILENO);
> > +
> > + /* close all other fds to the pipes */
> > + close(child_stdin);
> > + close(child_stdout);
> > + close(backtrace_handler_stdout);
> > + close(backtrace_handler_stdout);
> > +
> > + execl(BacktraceHandlerPath, BacktraceHandlerPath, pid_buffer, NULL);
> > + exit(1);
> > + } else {
> > + if (close(child_stdin) != 0)
> > + report_init_error("failed to close pipe fd");
> > + if (close(child_stdout) != 0)
> > + report_init_error("failed to close pipe fd");
> > + }
> > + }
> > +}
> > +
> > +void xorg_backtrace(void) {
> > + if (BacktraceHandlerPath) {
> > + int status;
> > +
> > + /* check that the handler process is still running */
> > + if (waitpid(child_pid, &status, WNOHANG) == 0) {
> > + char buffer[1];
> > +
> > + /* tell backtrace handler xorg has crashed */
> > + while (write(backtrace_handler_stdin, cmd_crash, sizeof(cmd_crash ) \
> > - 1) < 0) + if (errno != EAGAIN && errno != EINTR)
> > + break;
> > +
> > + /* exit to caller after backtrace handler writes anything to stdout \
> > */ + while (read(backtrace_handler_stdout, buffer, sizeof(buffer)) < \
> > 0) + if (errno != EAGAIN && errno != EINTR)
> > + break;
> > +
> > + } else {
> > + /* handler process has quit? run builtin handler */
> > + xorg_builtin_backtrace();
> > + }
> > + } else {
> > + xorg_builtin_backtrace();
> > + }
> > +}
> > +
> > +void xorg_cleanup_backtrace(void) {
> > + if (BacktraceHandlerPath) {
> > + int status;
> > +
> > + BacktraceHandlerPath = NULL;
> > +
> > + /* tell backtrace handler xorg is about to exit cleanly
> > + EPIPE is returned if the child process closes the pipe
> > + (which happens when the process exits) and the loop will exit */
> > + while (write(backtrace_handler_stdin, cmd_exit, sizeof(cmd_exit ) - 1) < \
> > 0) + if (errno != EAGAIN && errno != EINTR)
> > + break;
> > +
> > + /* If the child has already exited waitpid return with ECHILD
> > + and the loop will exit */
> > + while (waitpid(child_pid, &status, 0) < 0)
> > + if (errno != EINTR)
> > + break;
> > +
> > + }
> > +}
> > diff --git a/os/log.c b/os/log.c
> > index f519762..7b3409a 100644
> > --- a/os/log.c
> > +++ b/os/log.c
> > @@ -523,6 +523,9 @@ FatalError(const char *f, ...)
> > va_list args;
> > static Bool beenhere = FALSE;
> > 
> > + /* make sure any backtrace handler process is told to exit */
> > + xorg_cleanup_backtrace();
> > +
> > if (beenhere)
> > 	ErrorF("\nFatalError re-entered, aborting\n");
> > else
> > diff --git a/os/utils.c b/os/utils.c
> > index 36cb46f..78c39e6 100644
> > --- a/os/utils.c
> > +++ b/os/utils.c
> > @@ -470,6 +470,7 @@ void UseMsg(void)
> > ErrorF("-ac disable access control restrictions\n");
> > ErrorF("-audit int set audit trail level\n");	
> > ErrorF("-auth file select authorization file\n");	
> > + ErrorF("-backtrace string path of program to run to handle a server \
> > crash\n"); ErrorF("-br create root window with black \
> > background\n"); ErrorF("+bs enable any backing store \
> > support\n"); ErrorF("-bs disable any backing store \
> > support\n"); @@ -616,6 +617,13 @@ ProcessCommandLine(int argc, char *argv[])
> > 	 else
> > 		UseMsg();
> > 	}
> > + else if ( strcmp( argv[i], "-backtrace") == 0)
> > + {
> > +	 if(++i < argc)
> > + BacktraceHandlerPath = argv[i];
> > +	 else
> > +		UseMsg();
> > + }
> > 	else if ( strcmp( argv[i], "-br") == 0) ; /* default */
> > 	else if ( strcmp( argv[i], "+bs") == 0)
> > 	 enableBackingStore = TRUE;
> 
> 
> 


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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN" \
"http://www.w3.org/TR/REC-html40/strict.dtd"> <html><head><meta name="qrichtext" \
content="1" /><style type="text/css"> p, li { white-space: pre-wrap; }
</style></head><body style=" font-family:'Monospace'; font-size:10pt; \
font-weight:400; font-style:normal;"> On Wednesday 28 September 2011 18:37:04 Jeremy Huddleston \
wrote: &gt; After \
some thought, I think it's a good idea to not wait for the handler to exit. It may \
want to do some extra processing that it doesn't need the process hanging around \
for. &gt; &gt; You probably meant one of these to be \
backtrace_handler_stdin: &gt; &gt; + close(backtrace_handler_stdout); &gt; &gt; + \
close(backtrace_handler_stdout); Opss... V4 will fix this \
 &gt; &gt; I'd like to see a followup to set BacktraceHandlerPath from \
xorg.conf Can I leave that to someone else? \
Barry \
&gt; &gt; On Sep 28, 2011, at 3:09 \
AM, Barry Scott wrote: &gt; &gt; &gt; It is useful to be able to run an external program to \
analyse &gt; &gt; a \
crashed server process. The server will run a user supplied &gt; &gt; program in a \
subprocess of the server. &gt; &gt; &gt; &gt; The subprocess is created when the server starts up so \
that all &gt; &gt; \
resources needed to create the subprocess are available. It is not &gt; &gt; always possible to \
start up a process from within a crashed server. &gt; &gt; For example if the malloc heap is \
corrupt fork will not work. &gt; &gt; &gt; &gt; If the server crashes a &quot;crash&quot; message is \
sent to the handler on &gt; &gt; its stdin. The handler can then respond in whatever way \
it wishes. &gt; &gt; \
If the handler wants the server to continue, return from &gt; &gt; xorg_backtrace, it \
must write a line to its stdout. &gt; &gt; &gt; &gt; When the server exits normally the handler is sent the \
&quot;exit&quot; &gt; &gt; \
message just before the server exits. &gt; &gt; &gt; &gt; Signed-off-by: Barry Scott \
&lt;barry.scott@onelan.co.uk&gt; &gt; &gt; Reviewed-by: Simon Farnsworth \
&lt;simon.farnsworth@onelan.co.uk&gt; &gt; &gt; --- &gt; &gt; change from V2: &gt; &gt; * restore trailing \
NL in main.c &gt; &gt; * \
beef up comments to make it clea how loops are exited &gt; &gt; when the child process dies &gt; &gt; * Use _X_HIDDEN for \
new symbols that are not to be exported &gt; &gt; &gt; &gt; change from V1: &gt; &gt; &gt; &gt; * check for EAGAIN \
and EINTR on calls to read(), write() and waitpid() &gt; &gt; * put -backtrace into lexical position \
in the command parser and usage &gt; &gt; * fix coding style white space and condition \
ordering &gt; &gt; * \
update man page with more details &gt; &gt; * call xorg_cleanup_backtrace() from FatalError() &gt; &gt; &gt; &gt; dix/main.c | \
5 ++ &gt; &gt; \
include/os.h | 3 + &gt; &gt; man/Xserver.man | 20 +++++++++ &gt; &gt; os/backtrace.c | \
123 +++++++++++++++++++++++++++++++++++++++++++++++++++++- &gt; &gt; os/log.c | \
3 + &gt; &gt; \
os/utils.c | 8 ++++ &gt; &gt; 6 files changed, 159 insertions(+), 3 deletions(-) \
&gt; &gt; &gt; &gt; diff --git \
a/dix/main.c b/dix/main.c &gt; &gt; index 16575ce..3326e78 100644 &gt; &gt; --- \
a/dix/main.c &gt; &gt; \
+++ b/dix/main.c &gt; &gt; \
@@ -147,6 +147,8 @@ int main(int argc, char *argv[], char *envp[]) &gt; &gt; &gt; &gt; \
ProcessCommandLine(argc, argv); &gt; &gt; &gt; &gt; + xorg_init_backtrace(); &gt; &gt; + &gt; &gt; \
alwaysCheckForInput[0] = 0; &gt; &gt; alwaysCheckForInput[1] = 1; &gt; &gt; while(1) &gt; &gt; @@ -354,6 +356,9 @@ \
int main(int argc, char *argv[], char *envp[]) &gt; &gt; 	free(ConnectionInfo); &gt; &gt; 	ConnectionInfo = \
NULL; &gt; &gt; \
} &gt; &gt; \
+ &gt; &gt; + \
xorg_cleanup_backtrace(); &gt; &gt; + &gt; &gt; return 0; <p style=" margin-top:0px; \
margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; \
&gt; &gt; diff --git \
a/include/os.h b/include/os.h &gt; &gt; index a553f57..00336e5 100644 &gt; &gt; --- \
a/include/os.h &gt; &gt; \
+++ b/include/os.h &gt; &gt; \
@@ -541,6 +541,9 @@ extern _X_EXPORT void ErrorF(const char *f, ...) \
_X_ATTRIBUTE_PRINTF(1,2); &gt; &gt; extern _X_EXPORT void Error(const char *str); &gt; &gt; extern _X_EXPORT \
void LogPrintMarkers(void); &gt; &gt; &gt; &gt; +extern _X_HIDDEN void xorg_init_backtrace(void); &gt; &gt; extern _X_EXPORT \
void xorg_backtrace(void); &gt; &gt; +extern _X_HIDDEN void xorg_cleanup_backtrace(void); \
&gt; &gt; +extern _X_HIDDEN \
const char *BacktraceHandlerPath; &gt; &gt; &gt; &gt; #endif /* OS_H */ &gt; &gt; diff --git a/man/Xserver.man \
b/man/Xserver.man &gt; &gt; \
index f743912..9def022 100644 &gt; &gt; --- a/man/Xserver.man &gt; &gt; +++ b/man/Xserver.man &gt; &gt; @@ -100,6 +100,9 @@ \
specifies a file which contains a collection of authorization records used &gt; &gt; to authenticate \
access. See also the \fIxdm\fP(1) and &gt; &gt; \fIXsecurity\fP(__miscmansuffix__) \
manual pages. &gt; &gt; \
.TP 8 &gt; &gt; \
+.B \-backtrace \fIbacktrace-handler-path\fP &gt; &gt; +specifies the path to the optional \
backtrace handler program. See \fBBACKTRACE HANDLER\fP below. &gt; &gt; +.TP 8 &gt; &gt; .B \-br &gt; &gt; sets the default \
root window to solid black instead of the standard root weave &gt; &gt; pattern. This is \
the default unless -retro or -wr is specified. &gt; &gt; @@ -530,6 +533,23 @@ the following font \
path: &gt; &gt; \
/usr/share/fonts/default/ghostscript &gt; &gt; .fi &gt; &gt; &gt; &gt; +.SH BACKTRACE HANDLER &gt; &gt; + &gt; &gt; +The optional \
backtrace handler program will be run in a subprocess when &gt; &gt; +the server starts. \
The handler is invoked with argv[1] set to the PID &gt; &gt; +of the server. &gt; &gt; +.PP &gt; &gt; +The handler is \
expected to read a line from stdin that will tell the &gt; &gt; +handler what has happened to the \
server. &gt; &gt; \
+.PP &gt; &gt; \
+When the server is about to exit normally &quot;exit\\n&quot; is sent to the \
handler. &gt; &gt; \
+.PP &gt; &gt; \
+If the server crashes &quot;crash\n&quot; is sent to the handler and the server \
will &gt; &gt; \
+wait for a line to be written out on the handler's stdout. This causes &gt; &gt; +the server to \
return from the xorg_backtrace function. Typically after calling &gt; &gt; +xorg_backtrace \
additional error messages are logged and the server shuts down. &gt; &gt; +If you do not want \
the server to continue then kill it. &gt; &gt; + &gt; &gt; .SH FILES &gt; &gt; .TP 30 &gt; &gt; .I \
/etc/X\fBn\fP.hosts &gt; &gt; diff --git a/os/backtrace.c b/os/backtrace.c &gt; &gt; index \
7ca6dab..f9114eb 100644 &gt; &gt; --- a/os/backtrace.c &gt; &gt; +++ b/os/backtrace.c &gt; &gt; @@ -28,6 +28,11 \
@@ &gt; &gt; \
#include &quot;os.h&quot; &gt; &gt; #include &quot;misc.h&quot; &gt; &gt; &gt; &gt; +#include \
&lt;unistd.h&gt; &gt; &gt; \
+#include &lt;errno.h&gt; &gt; &gt; +#include &lt;sys/types.h&gt; &gt; &gt; +#include \
&lt;sys/wait.h&gt; &gt; &gt; \
+ &gt; &gt; \
#ifdef HAVE_BACKTRACE &gt; &gt; #ifndef _GNU_SOURCE &gt; &gt; #define _GNU_SOURCE &gt; &gt; @@ -35,7 +40,7 \
@@ &gt; &gt; \
#include &lt;dlfcn.h&gt; &gt; &gt; #include &lt;execinfo.h&gt; &gt; &gt; &gt; &gt; -void \
xorg_backtrace(void) &gt; &gt; +void xorg_builtin_backtrace(void) &gt; &gt; { &gt; &gt; void \
*array[64]; &gt; &gt; \
const char *mod; &gt; &gt; \
@@ -180,7 +185,7 @@ static int xorg_backtrace_pstack(void) { &gt; &gt; &gt; &gt; # if \
defined(HAVE_PSTACK) || defined(HAVE_WALKCONTEXT) &gt; &gt; &gt; &gt; -void xorg_backtrace(void) { &gt; &gt; +void \
xorg_builtin_backtrace(void) { &gt; &gt; <p style=" margin-top:0px; margin-bottom:0px; \
margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; \
&gt; &gt; @@ -207,7 +212,119 \
@@ void xorg_backtrace(void) { &gt; &gt; # else &gt; &gt; &gt; &gt; /* Default fallback if we can't find any way to get a \
backtrace */ &gt; &gt; \
-void xorg_backtrace(void) { return; } &gt; &gt; +void xorg_builtin_backtrace(void) { \
return; } &gt; &gt; \
 &gt; &gt; # endif &gt; &gt; #endif &gt; &gt; + &gt; &gt; +const char \
*BacktraceHandlerPath = NULL; &gt; &gt; + &gt; &gt; +static int backtrace_handler_stdin; &gt; &gt; +static int \
backtrace_handler_stdout; &gt; &gt; +static pid_t child_pid; &gt; &gt; + &gt; &gt; +static const char cmd_crash[] = \
&quot;crash\n&quot;; &gt; &gt; +static const char cmd_exit[] = &quot;exit\n&quot;; \
&gt; &gt; + &gt; &gt; +static void \
report_init_error(const char *msg) { &gt; &gt; + /* prevent any further use of the \
handler */ &gt; &gt; + \
BacktraceHandlerPath = NULL; &gt; &gt; + FatalError(&quot;%s - errno %d&quot;, msg, \
errno); &gt; &gt; \
+} &gt; &gt; \
+ &gt; &gt; \
+void xorg_init_backtrace(void) { &gt; &gt; + char pid_buffer[32]; &gt; &gt; + int pipe_fds[2]; &gt; &gt; + int \
child_stdin; &gt; &gt; + \
int child_stdout; &gt; &gt; \
+ &gt; &gt; + \
if (!BacktraceHandlerPath) &gt; &gt; + return; &gt; &gt; + &gt; &gt; + if (pipe(pipe_fds) != 0) &gt; &gt; + \
report_init_error(&quot;failed to create pipe&quot;); &gt; &gt; + backtrace_handler_stdin = \
pipe_fds[1]; &gt; &gt; + \
child_stdin = pipe_fds[0]; &gt; &gt; + &gt; &gt; + if (pipe(pipe_fds) != 0) &gt; &gt; + \
report_init_error(&quot;failed to create pipe&quot;); &gt; &gt; + backtrace_handler_stdout = \
pipe_fds[0]; &gt; &gt; + \
child_stdout = pipe_fds[1]; &gt; &gt; + &gt; &gt; + /* server pid will be passed in argv[1] */ &gt; &gt; + snprintf( \
pid_buffer, sizeof(pid_buffer), &quot;%d&quot;, getpid()); &gt; &gt; + &gt; &gt; + child_pid = \
fork(); &gt; &gt; + \
if (child_pid &lt; 0) { &gt; &gt; + report_init_error(&quot;failed to \
fork&quot;); &gt; &gt; + \
} else { &gt; &gt; + \
if (child_pid == 0) { &gt; &gt; + /* setup stdin, stdout to point to the \
pipes */ &gt; &gt; + \
dup2(child_stdin, STDIN_FILENO); &gt; &gt; + dup2(child_stdout, STDOUT_FILENO); &gt; &gt; + &gt; &gt; + /* \
close all other fds to the pipes */ &gt; &gt; + close(child_stdin); &gt; &gt; + \
close(child_stdout); &gt; &gt; + close(backtrace_handler_stdout); &gt; &gt; + \
close(backtrace_handler_stdout); &gt; &gt; + &gt; &gt; + execl(BacktraceHandlerPath, \
BacktraceHandlerPath, pid_buffer, NULL); &gt; &gt; + exit(1); &gt; &gt; + } else \
{ &gt; &gt; + \
if (close(child_stdin) != 0) &gt; &gt; + report_init_error(&quot;failed to close \
pipe fd&quot;); &gt; &gt; + \
if (close(child_stdout) != 0) &gt; &gt; + report_init_error(&quot;failed to close \
pipe fd&quot;); &gt; &gt; + \
} &gt; &gt; + \
} &gt; &gt; \
+} &gt; &gt; \
+ &gt; &gt; \
+void xorg_backtrace(void) { &gt; &gt; + if (BacktraceHandlerPath) { &gt; &gt; + int \
status; &gt; &gt; \
+ &gt; &gt; + \
/* check that the handler process is still running */ &gt; &gt; + if (waitpid(child_pid, \
&amp;status, WNOHANG) == 0) { &gt; &gt; + char buffer[1]; &gt; &gt; + &gt; &gt; + /* \
tell backtrace handler xorg has crashed */ &gt; &gt; + while \
(write(backtrace_handler_stdin, cmd_crash, sizeof(cmd_crash ) - 1) &lt; 0) &gt; &gt; + if \
(errno != EAGAIN &amp;&amp; errno != EINTR) &gt; &gt; + break; &gt; &gt; + <p style=" \
margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; \
&gt; &gt; + while \
(read(backtrace_handler_stdout, buffer, sizeof(buffer)) &lt; 0) &gt; &gt; + if \
(errno != EAGAIN &amp;&amp; errno != EINTR) &gt; &gt; + break; &gt; &gt; + &gt; &gt; + } else \
{ &gt; &gt; + \
/* handler process has quit? run builtin handler */ &gt; &gt; + \
xorg_builtin_backtrace(); &gt; &gt; + } &gt; &gt; + } else { &gt; &gt; + \
xorg_builtin_backtrace(); &gt; &gt; + } &gt; &gt; +} &gt; &gt; + &gt; &gt; +void xorg_cleanup_backtrace(void) { &gt; &gt; + if \
(BacktraceHandlerPath) { &gt; &gt; + int status; &gt; &gt; + &gt; &gt; + BacktraceHandlerPath = \
NULL; &gt; &gt; \
+ &gt; &gt; + \
/* tell backtrace handler xorg is about to exit cleanly &gt; &gt; + EPIPE \
is returned if the child process closes the pipe &gt; &gt; + (which happens when the \
process exits) and the loop will exit */ &gt; &gt; + while \
(write(backtrace_handler_stdin, cmd_exit, sizeof(cmd_exit ) - 1) &lt; 0) &gt; &gt; + if \
(errno != EAGAIN &amp;&amp; errno != EINTR) &gt; &gt; + break; &gt; &gt; + &gt; &gt; + /* If the \
child has already exited waitpid return with ECHILD &gt; &gt; + and the loop will exit \
*/ &gt; &gt; + \
while (waitpid(child_pid, &amp;status, 0) &lt; 0) &gt; &gt; + if (errno != EINTR) &gt; &gt; + \
break; &gt; &gt; \
+ &gt; &gt; + \
} &gt; &gt; \
+} &gt; &gt; \

diff --git a/os/log.c b/os/log.c</p> <p style=" margin-top:0px; margin-bottom:0px; \
margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; \
-qt-user-state:0;">&gt; &gt; index f519762..7b3409a 100644</p> <p style=" \
margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; \
-qt-block-indent:0; text-indent:0px; -qt-user-state:0;">&gt; &gt; --- a/os/log.c</p> \
<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; \
-qt-block-indent:0; text-indent:0px; -qt-user-state:0;">&gt; &gt; +++ b/os/log.c</p> \
<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; \
-qt-block-indent:0; text-indent:0px; -qt-user-state:0;">&gt; &gt; @@ -523,6 +523,9 @@ \
FatalError(const char *f, ...)</p> <p style=" margin-top:0px; margin-bottom:0px; \
margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; \
-qt-user-state:0;">&gt; &gt;     va_list args;</p> <p style=" margin-top:0px; \
margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; \
text-indent:0px; -qt-user-state:0;">&gt; &gt;     static Bool beenhere = FALSE;</p> \
<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; \
-qt-block-indent:0; text-indent:0px; -qt-user-state:0;">&gt; &gt; </p> <p style=" \
margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; \
-qt-block-indent:0; text-indent:0px; -qt-user-state:0;">&gt; &gt; +    /* make sure \
any backtrace handler process is told to exit */</p> <p style=" margin-top:0px; \
margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; \
text-indent:0px; -qt-user-state:0;">&gt; &gt; +    xorg_cleanup_backtrace();</p> <p \
style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; \
-qt-block-indent:0; text-indent:0px; -qt-user-state:0;">&gt; &gt; +</p> <p style=" \
margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; \
-qt-block-indent:0; text-indent:0px; -qt-user-state:0;">&gt; &gt;     if \
(beenhere)</p> <p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; \
margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">&gt; &gt; \
ErrorF(&quot;\nFatalError re-entered, aborting\n&quot;);</p> <p style=" \
margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; \
-qt-block-indent:0; text-indent:0px; -qt-user-state:0;">&gt; &gt;     else</p> <p \
style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; \
-qt-block-indent:0; text-indent:0px; -qt-user-state:0;">&gt; &gt; diff --git \
a/os/utils.c b/os/utils.c</p> <p style=" margin-top:0px; margin-bottom:0px; \
margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; \
-qt-user-state:0;">&gt; &gt; index 36cb46f..78c39e6 100644</p> <p style=" \
margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; \
-qt-block-indent:0; text-indent:0px; -qt-user-state:0;">&gt; &gt; --- \
a/os/utils.c</p> <p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; \
margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">&gt; &gt; \
+++ b/os/utils.c</p> <p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; \
margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">&gt; &gt; \
@@ -470,6 +470,7 @@ void UseMsg(void)</p> <p style=" margin-top:0px; \
margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; \
text-indent:0px; -qt-user-state:0;">&gt; &gt;     ErrorF(&quot;-ac                    \
disable access control restrictions\n&quot;);</p> <p style=" margin-top:0px; \
margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; \
text-indent:0px; -qt-user-state:0;">&gt; &gt;     ErrorF(&quot;-audit int             \
set audit trail level\n&quot;);	</p> <p style=" margin-top:0px; margin-bottom:0px; \
margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; \
-qt-user-state:0;">&gt; &gt;     ErrorF(&quot;-auth file             select \
authorization file\n&quot;);	</p> <p style=" margin-top:0px; margin-bottom:0px; \
margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; \
-qt-user-state:0;">&gt; &gt; +    ErrorF(&quot;-backtrace string      path of program \
to run to handle a server crash\n&quot;);</p> <p style=" margin-top:0px; \
margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; \
text-indent:0px; -qt-user-state:0;">&gt; &gt;     ErrorF(&quot;-br                    \
create root window with black background\n&quot;);</p> <p style=" margin-top:0px; \
margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; \
text-indent:0px; -qt-user-state:0;">&gt; &gt;     ErrorF(&quot;+bs                    \
enable any backing store support\n&quot;);</p> <p style=" margin-top:0px; \
margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; \
text-indent:0px; -qt-user-state:0;">&gt; &gt;     ErrorF(&quot;-bs                    \
disable any backing store support\n&quot;);</p> <p style=" margin-top:0px; \
margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; \
text-indent:0px; -qt-user-state:0;">&gt; &gt; @@ -616,6 +617,13 @@ \
ProcessCommandLine(int argc, char *argv[])</p> <p style=" margin-top:0px; \
margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; \
text-indent:0px; -qt-user-state:0;">&gt; &gt; 	    else</p> <p style=" \
margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; \
-qt-block-indent:0; text-indent:0px; -qt-user-state:0;">&gt; &gt; 		UseMsg();</p> <p \
style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; \
-qt-block-indent:0; text-indent:0px; -qt-user-state:0;">&gt; &gt; 	}</p> <p style=" \
margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; \
-qt-block-indent:0; text-indent:0px; -qt-user-state:0;">&gt; &gt; +        else if ( \
strcmp( argv[i], &quot;-backtrace&quot;) == 0)</p> <p style=" margin-top:0px; \
margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; \
text-indent:0px; -qt-user-state:0;">&gt; &gt; +        {</p> <p style=" \
margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; \
-qt-block-indent:0; text-indent:0px; -qt-user-state:0;">&gt; &gt; +	    if(++i &lt; \
argc)</p> <p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; \
margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">&gt; &gt; + \
BacktraceHandlerPath = argv[i];</p> <p style=" margin-top:0px; margin-bottom:0px; \
margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; \
-qt-user-state:0;">&gt; &gt; +	    else</p> <p style=" margin-top:0px; \
margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; \
text-indent:0px; -qt-user-state:0;">&gt; &gt; +		UseMsg();</p> <p style=" \
margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; \
-qt-block-indent:0; text-indent:0px; -qt-user-state:0;">&gt; &gt; +        }</p> <p \
style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; \
-qt-block-indent:0; text-indent:0px; -qt-user-state:0;">&gt; &gt; 	else if ( strcmp( \
argv[i], &quot;-br&quot;) == 0) ; /* default */</p> <p style=" margin-top:0px; \
margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; \
text-indent:0px; -qt-user-state:0;">&gt; &gt; 	else if ( strcmp( argv[i], \
&quot;+bs&quot;) == 0)</p> <p style=" margin-top:0px; margin-bottom:0px; \
margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; \
-qt-user-state:0;">&gt; &gt; 	    enableBackingStore = TRUE;</p> <p style=" \
margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; \
-qt-block-indent:0; text-indent:0px; -qt-user-state:0;">&gt; </p> <p style=" \
margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; \
-qt-block-indent:0; text-indent:0px; -qt-user-state:0;">&gt; </p> <p style=" \
margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; \
-qt-block-indent:0; text-indent:0px; -qt-user-state:0;">&gt; </p> <p \
style="-qt-paragraph-type:empty; margin-top:0px; margin-bottom:0px; margin-left:0px; \
margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;"><br \
/></p></body></html>



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