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Full Discussion: Blocking file read
Top Forums Programming Blocking file read Post 302078507 by Hitori on Saturday 1st of July 2006 08:26:34 AM
Old 07-01-2006
There are two types of locking mechanisms: mandatory and advisory. Mandatory systems will actually prevent read()'s and write()'s to file. Several Unix systems support them.

To make an advisory lock in POSIX-systems fcntl must be used:
Code:
#include <fcntl.h>
...

struct flock fl;
int fd;

fl.l_type   = F_RDLCK;  /* read lock */
fl.l_whence = SEEK_SET; /* beginning of file */
fl.l_start  = 0;        /* offset from l_whence */
fl.l_len    = 0;        /* length, 0 = to EOF */
fl.l_pid    = getpid(); /* PID */

fd = open("filename", O_RDONLY);

fcntl(fd, F_SETLKW, &fl); /* set lock */

...


fl.l_type   = F_UNLCK;
fcntl(fd, F_SETLK, &fl); /* unset lock */

Note that there are no guarantees with advisory locks, mandatory locks are not supported by all systems however
 

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LEARN ABOUT OPENSOLARIS

grablogs.conf

grablogs.conf(4)						   File Formats 						  grablogs.conf(4)

NAME

       grablogs.conf - grablogs configuration for libgrablogs.so of the plugins of
	gnome-system-log file

SYNOPSIS

       /usr/lib/gnome-system-log/plugins/grablogs.conf

DESCRIPTION

       The  libgrablogs.so  is	a plugin for gnome-system-log(1), it colloct the log files from the system as many as possible. grablogs.conf is a
       configuration file that contains a set of lines mixed with sh(1) syntax codes and individual
	log files. libgrablogs.so will read the file try to get a log files list for
	gnome-system-log(1). Users can copy the file into $HOME/.gnome2/gnome-system-log/plugins/`uname -p` to overwrite the system default one.

       The grablogs.conf file contains the following configuration categories:

	      [configs]
		     Each line under this category is interpreted as a config file of System. The plugin will open the config file and try to find
		     all system paths of the logs.

	      [commands]
		     Each line under this category is interpreted as a shell command and will be execute through a pipe. And each line of the out-
		     put of the command will be interpreted as a log path.

	      [logs] Each line under this category is interpreted as a log path.

FILES

       /usr/lib/gnome-system-log/plugins/grablogs.conf
	      The system default configuration file for the plugin libgrablogs.so

       $HOME/.gnome2/gnome-system-log/plugins/`uname -p`/grablogs.conf
	      The user specific configuration file for the plugin libgrablogs.so

EMAMPLE

       [configs]
       /etc/syslog.conf
       [commands]
       for i in `svcs -aH -o FMRI | grep -v lrc `; do svcprop -p restarter/logfile $i  2>/dev/null  ||	svcprop  -q  -p  restarter/alt_logfile	$i
       2>/dev/null ; done
       [logs]
       /var/log/messages
       /var/log/secure
       /var/log/maillog
       /var/log/cron
       /var/log/Xorg.0.log
       /var/log/XFree86.0.log
       /var/log/auth.log
       /var/log/cups/error_log

SEE ALSO

       gnome-system-log(1), pipelog.conf(1)

gnome-utils 2.16.0						    13 Oct 2006 						  grablogs.conf(4)
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