Mention atomic_o_trunc capability in description of open() handler.

1 files changed, 12 insertions, 6 deletions

diff --git a/include/fuse_lowlevel.h b/include/fuse_lowlevel.h
index bad1d45..0f8c030 100644
--- a/include/fuse_lowlevel.h
+++ b/include/fuse_lowlevel.h
@@ -420,12 +420,18 @@ struct fuse_lowlevel_ops {
 	/**
 	 * Open a file
 	 *
-	 * Open flags (with the exception of O_CREAT, O_EXCL, O_NOCTTY and
-	 * O_TRUNC) are available in fi->flags.
-	 *
-	 * Filesystem may store an arbitrary file handle (pointer, index,
-	 * etc) in fi->fh, and use this in other all other file operations
-	 * (read, write, flush, release, fsync).
+	 * Open flags are available in fi->flags.  Creation (O_CREAT,
+	 * O_EXCL, O_NOCTTY) and by default also truncation (O_TRUNC)
+	 * flags will be filtered out. If an application specifies
+	 * O_TRUNC, fuse first calls truncate() and then open().
+	 *
+	 * If filesystem is able to handle O_TRUNC directly, the
+	 * init() handler should set the `FUSE_CAP_ATOMIC_O_TRUNC` bit
+	 * in ``conn->want``.
+	 *
+	 * Filesystem may store an arbitrary file handle (pointer,
+	 * index, etc) in fi->fh, and use this in other all other file
+	 * operations (read, write, flush, release, fsync).
 	 *
 	 * Filesystem may also implement stateless file I/O and not store
 	 * anything in fi->fh.