[PATCH 5.10 07/63] fs: expose LOOKUP_CACHED through openat2() RESOLVE_CACHED

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Jens Axboe <axboe@kernel.dk>

[ Upstream commit 99668f618062816ca7ba639b007eb145b9d3d41e ]

Now that we support non-blocking path resolution internally, expose it
via openat2() in the struct open_how ->resolve flags. This allows
applications using openat2() to limit path resolution to the extent that
it is already cached.

If the lookup cannot be satisfied in a non-blocking manner, openat2(2)
will return -1/-EAGAIN.

Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 fs/open.c                    |    6 ++++++
 include/linux/fcntl.h        |    2 +-
 include/uapi/linux/openat2.h |    4 ++++
 3 files changed, 11 insertions(+), 1 deletion(-)

--- a/fs/open.c
+++ b/fs/open.c
@@ -1099,6 +1099,12 @@ inline int build_open_flags(const struct
 		lookup_flags |= LOOKUP_BENEATH;
 	if (how->resolve & RESOLVE_IN_ROOT)
 		lookup_flags |= LOOKUP_IN_ROOT;
+	if (how->resolve & RESOLVE_CACHED) {
+		/* Don't bother even trying for create/truncate/tmpfile open */
+		if (flags & (O_TRUNC | O_CREAT | O_TMPFILE))
+			return -EAGAIN;
+		lookup_flags |= LOOKUP_CACHED;
+	}
 
 	op->lookup_flags = lookup_flags;
 	return 0;
--- a/include/linux/fcntl.h
+++ b/include/linux/fcntl.h
@@ -19,7 +19,7 @@
 /* List of all valid flags for the how->resolve argument: */
 #define VALID_RESOLVE_FLAGS \
 	(RESOLVE_NO_XDEV | RESOLVE_NO_MAGICLINKS | RESOLVE_NO_SYMLINKS | \
-	 RESOLVE_BENEATH | RESOLVE_IN_ROOT)
+	 RESOLVE_BENEATH | RESOLVE_IN_ROOT | RESOLVE_CACHED)
 
 /* List of all open_how "versions". */
 #define OPEN_HOW_SIZE_VER0	24 /* sizeof first published struct */
--- a/include/uapi/linux/openat2.h
+++ b/include/uapi/linux/openat2.h
@@ -35,5 +35,9 @@ struct open_how {
 #define RESOLVE_IN_ROOT		0x10 /* Make all jumps to "/" and ".."
 					be scoped inside the dirfd
 					(similar to chroot(2)). */
+#define RESOLVE_CACHED		0x20 /* Only complete if resolution can be
+					completed through cached lookup. May
+					return -EAGAIN if that's not
+					possible. */
 
 #endif /* _UAPI_LINUX_OPENAT2_H */