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/*++
/* NAME
/* open_lock 3
/* SUMMARY
/* open or create file and lock it for exclusive access
/* SYNOPSIS
/* #include <open_lock.h>
/*
/* VSTREAM *open_lock(path, flags, mode, why)
/* const char *path;
/* int flags;
/* mode_t mode;
/* VSTRING *why;
/* DESCRIPTION
/* This module opens or creates the named file and attempts to
/* acquire an exclusive lock. The lock is lost when the last
/* process closes the file.
/*
/* Arguments:
/* .IP "path, flags, mode"
/* These are passed on to safe_open().
/* .IP why
/* storage for diagnostics.
/* SEE ALSO
/* safe_open(3) carefully open or create file
/* myflock(3) get exclusive lock on file
/* DIAGNOSTICS
/* In case of problems the result is a null pointer and a problem
/* description is returned via the global \fIerrno\fR variable.
/* LICENSE
/* .ad
/* .fi
/* The Secure Mailer license must be distributed with this software.
/* AUTHOR(S)
/* Wietse Venema
/* IBM T.J. Watson Research
/* P.O. Box 704
/* Yorktown Heights, NY 10598, USA
/*--*/
/* System library. */
#include <sys_defs.h>
#include <unistd.h>
#include <fcntl.h>
/* Utility library. */
#include <msg.h>
#include <vstream.h>
#include <vstring.h>
#include <safe_open.h>
#include <myflock.h>
#include <open_lock.h>
/* open_lock - open file and lock it for exclusive access */
VSTREAM *open_lock(const char *path, int flags, mode_t mode, VSTRING *why)
{
VSTREAM *fp;
/*
* Carefully create or open the file, and lock it down. Some systems
* don't have the O_LOCK open() flag, or the flag does not do what we
* want, so we roll our own lock.
*/
if ((fp = safe_open(path, flags, mode, (struct stat *) 0, -1, -1, why)) == 0)
return (0);
if (myflock(vstream_fileno(fp), INTERNAL_LOCK,
MYFLOCK_OP_EXCLUSIVE | MYFLOCK_OP_NOWAIT) < 0) {
vstring_sprintf(why, "unable to set exclusive lock: %m");
vstream_fclose(fp);
return (0);
}
return (fp);
}
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