[PATCH v5 2/2] fuse: add new function to invalidate cache for all inodes

[Luis Henriques <luis@igalia.com>]

Currently userspace is able to notify the kernel to invalidate the cache
for an inode.  This means that, if all the inodes in a filesystem need to
be invalidated, then userspace needs to iterate through all of them and do
this kernel notification separately.

This patch adds a new option that allows userspace to invalidate all the
inodes with a single notification operation.  In addition to invalidate
all the inodes, it also shrinks the sb dcache.

Signed-off-by: Luis Henriques <luis@igalia.com>
---
 fs/fuse/inode.c           | 33 +++++++++++++++++++++++++++++++++
 include/uapi/linux/fuse.h |  3 +++
 2 files changed, 36 insertions(+)

diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index e9db2cb8c150..01a4dc5677ae 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -547,6 +547,36 @@ struct inode *fuse_ilookup(struct fuse_conn *fc, u64 nodeid,
 	return NULL;
 }
 
+static int fuse_reverse_inval_all(struct fuse_conn *fc)
+{
+	struct fuse_mount *fm;
+	struct inode *inode;
+
+	inode = fuse_ilookup(fc, FUSE_ROOT_ID, &fm);
+	if (!inode || !fm)
+		return -ENOENT;
+
+	/* Remove all possible active references to cached inodes */
+	shrink_dcache_sb(fm->sb);
+
+	/* Remove all unreferenced inodes from cache */
+	invalidate_inodes(fm->sb);
+
+	return 0;
+}
+
+/*
+ * Notify to invalidate inodes cache.  It can be called with @nodeid set to
+ * either:
+ *
+ * - An inode number - Any pending writebacks within the rage [@offset @len]
+ *   will be triggered and the inode will be validated.  To invalidate the whole
+ *   cache @offset has to be set to '0' and @len needs to be <= '0'; if @offset
+ *   is negative, only the inode attributes are invalidated.
+ *
+ * - FUSE_INVAL_ALL_INODES - All the inodes in the superblock are invalidated
+ *   and the whole dcache is shrinked.
+ */
 int fuse_reverse_inval_inode(struct fuse_conn *fc, u64 nodeid,
 			     loff_t offset, loff_t len)
 {
@@ -555,6 +585,9 @@ int fuse_reverse_inval_inode(struct fuse_conn *fc, u64 nodeid,
 	pgoff_t pg_start;
 	pgoff_t pg_end;
 
+	if (nodeid == FUSE_INVAL_ALL_INODES)
+		return fuse_reverse_inval_all(fc);
+
 	inode = fuse_ilookup(fc, nodeid, NULL);
 	if (!inode)
 		return -ENOENT;
diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
index 5e0eb41d967e..e5852b63f99f 100644
--- a/include/uapi/linux/fuse.h
+++ b/include/uapi/linux/fuse.h
@@ -669,6 +669,9 @@ enum fuse_notify_code {
 	FUSE_NOTIFY_CODE_MAX,
 };
 
+/* The nodeid to request to invalidate all inodes */
+#define FUSE_INVAL_ALL_INODES 0
+
 /* The read buffer is required to be at least 8k, but may be much larger */
 #define FUSE_MIN_READ_BUFFER 8192