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List:       sylpheed
Subject:    [sylpheed:27883] Re: patch for locking data files
From:       Jean-Yves Lefort <jylefort () FreeBSD ! org>
Date:       2006-05-09 2:22:20
Message-ID: 20060509042220.fae22541.jylefort () FreeBSD ! org
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On Tue, 9 May 2006 01:45:05 +0200
Jean-Yves Lefort <jylefort@FreeBSD.org> wrote:

> Could you please commit the attached patch? It allows applications to
> reliably read the Sylpheed data files while Sylpheed is running (using
> POSIX file locking).
> 
> For instance, in Mail Notification [1], I read .sylpheed_mark files to
> check for the MSG_NEW and MSG_UNREAD flags. Without locking, races
> happen rather frequently and cause various inconveniences.
> 
> Thanks
> 
> [1] http://www.nongnu.org/mailnotify/

I forgot to create the file if it does not already exist (O_CREAT) and
to truncate it otherwise. The revised patch is attached.

-- 
Jean-Yves Lefort

jylefort@FreeBSD.org
http://lefort.be.eu.org/

["sylpheed-2.2.4-flock.diff" (text/plain)]

--- libsylph/procmsg.c.orig	Fri Mar 10 03:26:28 2006
+++ libsylph/procmsg.c	Tue May  9 04:16:46 2006
@@ -23,6 +23,9 @@
 #include <glib/gi18n.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
+#include <fcntl.h>
+#include <unistd.h>
 
 #include "utils.h"
 #include "procmsg.h"
@@ -759,6 +762,20 @@
 	fclose(fp);
 }
 
+/* play nice with other applications who'd like to read our data files */
+static void procmsg_lock_data_file(int fd)
+{
+	struct flock lock;
+
+	memset(&lock, 0, sizeof(lock));
+	lock.l_start = 0;		/* from l_whence */
+	lock.l_len = 0;			/* to end of file */
+	lock.l_type = F_WRLCK;		/* write lock */
+	lock.l_whence = SEEK_CUR;	/* from current position */
+
+	fcntl(fd, F_SETLKW, &lock);
+}
+
 FILE *procmsg_open_data_file(const gchar *file, guint version,
 			     DataOpenMode mode, gchar *buf, size_t buf_size)
 {
@@ -768,8 +785,21 @@
 	g_return_val_if_fail(file != NULL, NULL);
 
 	if (mode == DATA_WRITE) {
-		if ((fp = g_fopen(file, "wb")) == NULL) {
-			FILE_OP_ERROR(file, "fopen");
+		int fd;
+
+		if ((fd = g_open(file, O_WRONLY | O_CREAT, S_IRUSR | S_IWUSR)) < 0) {
+			FILE_OP_ERROR(file, "open");
+			return NULL;
+		}
+		procmsg_lock_data_file(fd);
+		if (ftruncate(fd, 0) < 0) {
+			close(fd);
+			FILE_OP_ERROR(file, "ftruncate");
+			return NULL;
+		}
+		if ((fp = fdopen(fd, "wb")) == NULL) {
+			close(fd);
+			FILE_OP_ERROR(file, "fdopen");
 			return NULL;
 		}
 		if (change_file_mode_rw(fp, file) < 0)
@@ -800,8 +830,10 @@
 	if (fp) {
 		/* reopen with append mode */
 		fclose(fp);
-		if ((fp = g_fopen(file, "ab")) == NULL)
+		if ((fp = g_fopen(file, "ab")) == NULL) {
 			FILE_OP_ERROR(file, "fopen");
+		} else
+			procmsg_lock_data_file(fileno(fp));
 	} else {
 		/* open with overwrite mode if mark file doesn't exist or
 		   version is different */

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