From a5388cc58647a6506e62acddc648ed6ca7b76fa5 Mon Sep 17 00:00:00 2001
From: Eric Biggers <ebiggers3@gmail.com>
Date: Mon, 26 May 2014 15:42:50 -0500
Subject: [PATCH] Fix file locking

- Lock in_fd only
- Unlock WIM immediately after commiting mounted image (before
  fuse_main() returns)
- Don't lock WIM for read-only mount
---
 include/wimlib/write.h |  9 ++++-----
 src/mount_image.c      | 14 +++++++++-----
 src/write.c            | 20 +++++++++++---------
 3 files changed, 24 insertions(+), 19 deletions(-)

diff --git a/include/wimlib/write.h b/include/wimlib/write.h
index c15e6ced..273a6a71 100644
--- a/include/wimlib/write.h
+++ b/include/wimlib/write.h
@@ -32,19 +32,18 @@
 
 #if defined(HAVE_SYS_FILE_H) && defined(HAVE_FLOCK)
 extern int
-lock_wim_for_append(WIMStruct *wim, int fd);
+lock_wim_for_append(WIMStruct *wim);
 extern void
-unlock_wim_for_append(WIMStruct *wim, int fd);
+unlock_wim_for_append(WIMStruct *wim);
 #else
 static inline int
-lock_wim_for_append(WIMStruct *wim, int fd)
+lock_wim_for_append(WIMStruct *wim)
 {
 	return 0;
 }
 static inline void
-unlock_wim_for_append(WIMStruct *wim, int fd)
+unlock_wim_for_append(WIMStruct *wim)
 {
-	return 0;
 }
 #endif
 
diff --git a/src/mount_image.c b/src/mount_image.c
index 1c31cae2..3aac49d1 100644
--- a/src/mount_image.c
+++ b/src/mount_image.c
@@ -1189,8 +1189,10 @@ out:
 	/* Leave the image mounted if commit failed, unless this is a
 	 * forced unmount.  The user can retry without commit if they
 	 * want.  */
-	if (!ret || (unmount_flags & WIMLIB_UNMOUNT_FLAG_FORCE))
+	if (!ret || (unmount_flags & WIMLIB_UNMOUNT_FLAG_FORCE)) {
+		unlock_wim_for_append(wimfs_ctx->wim);
 		fuse_exit(fuse_ctx->fuse);
+	}
 	if (mq != (mqd_t)-1)
 		mq_close(mq);
 	return ret;
@@ -2098,9 +2100,11 @@ wimlib_mount_image(WIMStruct *wim, int image, const char *dir,
 		return WIMLIB_ERR_INVALID_PARAM;
 	}
 
-	ret = lock_wim_for_append(wim, wim->in_fd.fd);
-	if (ret)
-		return ret;
+	if (mount_flags & WIMLIB_MOUNT_FLAG_READWRITE) {
+		ret = lock_wim_for_append(wim);
+		if (ret)
+			return ret;
+	}
 
 	/* If the user did not specify an interface for accessing named
 	 * data streams, use the default (extended attributes).  */
@@ -2255,7 +2259,7 @@ wimlib_mount_image(WIMStruct *wim, int image, const char *dir,
 	if (mount_flags & WIMLIB_MOUNT_FLAG_READWRITE)
 		delete_staging_dir(&ctx);
 out_unlock:
-	unlock_wim_for_append(wim, wim->in_fd.fd);
+	unlock_wim_for_append(wim);
 	return ret;
 }
 
diff --git a/src/write.c b/src/write.c
index 0114618f..52178381 100644
--- a/src/write.c
+++ b/src/write.c
@@ -2400,12 +2400,14 @@ finish_write(WIMStruct *wim, int image, int write_flags,
 }
 
 #if defined(HAVE_SYS_FILE_H) && defined(HAVE_FLOCK)
+
+/* Set advisory lock on WIM file (if not already done so)  */
 int
-lock_wim_for_append(WIMStruct *wim, int fd)
+lock_wim_for_append(WIMStruct *wim)
 {
 	if (wim->locked_for_append)
 		return 0;
-	if (!flock(fd, LOCK_EX | LOCK_NB)) {
+	if (!flock(wim->in_fd.fd, LOCK_EX | LOCK_NB)) {
 		wim->locked_for_append = 1;
 		return 0;
 	}
@@ -2413,11 +2415,13 @@ lock_wim_for_append(WIMStruct *wim, int fd)
 		return 0;
 	return WIMLIB_ERR_ALREADY_LOCKED;
 }
+
+/* Remove advisory lock on WIM file (if present)  */
 void
-unlock_wim_for_append(WIMStruct *wim, int fd)
+unlock_wim_for_append(WIMStruct *wim)
 {
 	if (wim->locked_for_append) {
-		flock(fd, LOCK_UN);
+		flock(wim->in_fd.fd, LOCK_UN);
 		wim->locked_for_append = 0;
 	}
 }
@@ -3060,7 +3064,7 @@ overwrite_wim_inplace(WIMStruct *wim, int write_flags, unsigned num_threads)
 	if (ret)
 		goto out_restore_memory_hdr;
 
-	ret = lock_wim_for_append(wim, wim->out_fd.fd);
+	ret = lock_wim_for_append(wim);
 	if (ret)
 		goto out_close_wim;
 
@@ -3096,8 +3100,7 @@ overwrite_wim_inplace(WIMStruct *wim, int write_flags, unsigned num_threads)
 	if (ret)
 		goto out_truncate;
 
-	/* lock was dropped when file descriptor was closed  */
-	wim->locked_for_append = 0;
+	unlock_wim_for_append(wim);
 	return 0;
 
 out_truncate:
@@ -3111,8 +3114,7 @@ out_truncate:
 out_restore_physical_hdr:
 	(void)write_wim_header_flags(hdr_save.flags, &wim->out_fd);
 out_unlock_wim:
-	/* lock is dropped when close_wim_writable() closes the file  */
-	wim->locked_for_append = 0;
+	unlock_wim_for_append(wim);
 out_close_wim:
 	(void)close_wim_writable(wim, write_flags);
 out_restore_memory_hdr:
-- 
2.43.0