1 /* $NetBSD: open_lock.c,v 1.1.1.1 2009/06/23 10:09:00 tron Exp $ */
2
3 /*++
4 /* NAME
5 /* open_lock 3
6 /* SUMMARY
7 /* open or create file and lock it for exclusive access
8 /* SYNOPSIS
9 /* #include <open_lock.h>
10 /*
11 /* VSTREAM *open_lock(path, flags, mode, why)
12 /* const char *path;
13 /* int flags;
14 /* mode_t mode;
15 /* VSTRING *why;
16 /* DESCRIPTION
17 /* This module opens or creates the named file and attempts to
18 /* acquire an exclusive lock. The lock is lost when the last
19 /* process closes the file.
20 /*
21 /* Arguments:
22 /* .IP "path, flags, mode"
23 /* These are passed on to safe_open().
24 /* .IP why
25 /* storage for diagnostics.
26 /* SEE ALSO
27 /* safe_open(3) carefully open or create file
28 /* myflock(3) get exclusive lock on file
29 /* DIAGNOSTICS
30 /* In case of problems the result is a null pointer and a problem
31 /* description is returned via the global \fIerrno\fR variable.
32 /* LICENSE
33 /* .ad
34 /* .fi
35 /* The Secure Mailer license must be distributed with this software.
36 /* AUTHOR(S)
37 /* Wietse Venema
38 /* IBM T.J. Watson Research
39 /* P.O. Box 704
40 /* Yorktown Heights, NY 10598, USA
41 /*--*/
42
43 /* System library. */
44
45 #include <sys_defs.h>
46 #include <unistd.h>
47 #include <fcntl.h>
48
49 /* Utility library. */
50
51 #include <msg.h>
52 #include <vstream.h>
53 #include <vstring.h>
54 #include <safe_open.h>
55 #include <myflock.h>
56 #include <open_lock.h>
57
58 /* open_lock - open file and lock it for exclusive access */
59
open_lock(const char * path,int flags,mode_t mode,VSTRING * why)60 VSTREAM *open_lock(const char *path, int flags, mode_t mode, VSTRING *why)
61 {
62 VSTREAM *fp;
63
64 /*
65 * Carefully create or open the file, and lock it down. Some systems
66 * don't have the O_LOCK open() flag, or the flag does not do what we
67 * want, so we roll our own lock.
68 */
69 if ((fp = safe_open(path, flags, mode, (struct stat *) 0, -1, -1, why)) == 0)
70 return (0);
71 if (myflock(vstream_fileno(fp), INTERNAL_LOCK,
72 MYFLOCK_OP_EXCLUSIVE | MYFLOCK_OP_NOWAIT) < 0) {
73 vstring_sprintf(why, "unable to set exclusive lock: %m");
74 vstream_fclose(fp);
75 return (0);
76 }
77 return (fp);
78 }
79