Patch by Vasilis Kaoutsis: Added and implemented lockf() using fcntl() locking.

Small change and notes on standard compliance by myself.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@22628 a95241bf-73f2-0310-859d-f6bbb57e9c96

headers/posix/unistd.h

@@ -21,6 +21,12 @@
 #define STDOUT_FILENO	1
 #define STDERR_FILENO	2
 
+/* function arguments needed by lockf() */
+#define F_ULOCK		0	/* unlock locked sections */
+#define F_LOCK		1	/* lock a section for exclusive use */
+#define F_TLOCK		2	/* test and lock a section for exclusive use */
+#define F_TEST		3	/* test a section for locks by other processes */
+
 /* POSIX version support */
 #define _POSIX_VERSION			(199009L)
 
@@ -111,7 +117,8 @@ extern int      getdtablesize(void);
 extern long		sysconf(int name);
 extern long		fpathconf(int fd, int name);
 extern long		pathconf(const char *path, int name);
-extern size_t		confstr(int name, char *buf, size_t len);
+extern size_t	confstr(int name, char *buf, size_t len);
+extern int		lockf(int fd, int function, off_t size);
 
 /* process functions */
 extern pid_t	fork(void);

src/system/libroot/posix/unistd/Jamfile

@@ -17,6 +17,7 @@ MergeObject posix_unistd.o :
 	hostname.cpp
 	ioctl.c
 	link.c
+	lockf.cpp
 	lseek.c
 	mknod.c
 	mount.c

src/system/libroot/posix/unistd/lockf.cpp

@@ -0,0 +1,85 @@
+/*
+ * Copyright 2007, Vasilis Kaoutsis, kaoutsis@sch.gr.
+ * Distributed under the terms of the MIT License.
+ */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+
+int
+lockf(int fileDescriptor, int function, off_t size)
+{
+	struct flock fileLock;
+	fileLock.l_start = 0;
+	fileLock.l_len = size;
+	fileLock.l_whence = SEEK_CUR;
+
+	if (function == F_ULOCK) {
+		// unlock locked sections
+		fileLock.l_type = F_UNLCK;
+		return fcntl(fileDescriptor, F_SETLK, &fileLock);
+	} else if (function == F_LOCK) {
+		// lock a section for exclusive use
+		fileLock.l_type = F_WRLCK;
+		return fcntl(fileDescriptor, F_SETLKW, &fileLock);
+	} else if (function == F_TLOCK) {
+		// test and lock a section for exclusive use
+		fileLock.l_type = F_WRLCK;
+		return fcntl(fileDescriptor, F_SETLK, &fileLock);
+	} else if (function == F_TEST) {
+		// test a section for locks by other processes
+		fileLock.l_type = F_WRLCK;
+		if (fcntl(fileDescriptor, F_GETLK, &fileLock) == -1)
+			return -1;
+		if (fileLock.l_type == F_UNLCK)
+			return 0;
+
+		errno = EAGAIN;
+		return -1;
+	} else {
+		errno = EINVAL;
+		return -1;
+	}
+
+	// Notes regarding standard compliance (cf. Open Group Base Specs):
+	// * "The interaction between fcntl() and lockf() locks is unspecified."
+	// * fcntl() locking works on a per-process level. The lockf() description
+	//   is a little fuzzy on whether it works the same way. The first quote
+	//   seem to describe per-thread locks (though it might actually mean
+	//   "threads of other processes"), but the others quotes are strongly
+	//   indicating per-process locks:
+	//   - "Calls to lockf() from other threads which attempt to lock the locked
+	//     file section shall either return an error value or block until the
+	//     section becomes unlocked."
+	//   - "All the locks for a process are removed when the process
+	//     terminates."
+	//   - "F_TEST shall detect if a lock by another process is present on the
+	//     specified section."
+	//   - "The sections locked with F_LOCK or F_TLOCK may, in whole or in part,
+	//     contain or be contained by a previously locked section for the same
+	//     process. When this occurs, or if adjacent locked sections would
+	//     occur, the sections shall be combined into a single locked section."
+	// * fcntl() and lockf() handle a 0 size argument differently. The former
+	//   use the file size at the time of the call:
+	//    "If the command is F_SETLKW and the process must wait for another
+	//     process to release a lock, then the range of bytes to be locked shall
+	//     be determined before the fcntl() function blocks. If the file size
+	//     or file descriptor seek offset change while fcntl() is blocked, this
+	//     shall not affect the range of bytes locked."
+	//   lockf(), on the other hand, is supposed to create a lock whose size
+	//   dynamically adjusts to the file size:
+	//    "If size is 0, the section from the current offset through the largest
+	//     possible file offset shall be locked (that is, from the current
+	//     offset through the present or any future end-of-file)."
+	// * The lock release handling when closing descriptors sounds a little
+	//   different, though might actually mean the same.
+	//   For fcntl():
+	//    "All locks associated with a file for a given process shall be removed
+	//     when a file descriptor for that file is closed by that process or the
+	//     process holding that file descriptor terminates."
+	//   For lockf():
+	//    "File locks shall be released on first close by the locking process of
+	//     any file descriptor for the file."
+}