[RFC PATCH] 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 superblock dcache.

Signed-off-by: Luis Henriques <luis@igalia.com>
---
Just an additional note that this patch could eventually be simplified if
Dave Chinner patch to iterate through the superblock inodes[1] is merged.

[1] https://lore.kernel.org/r/20241002014017.3801899-3-david@fromorbit.com

 fs/fuse/inode.c           | 53 +++++++++++++++++++++++++++++++++++++++
 include/uapi/linux/fuse.h |  3 +++
 2 files changed, 56 insertions(+)

diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 3ce4f4e81d09..1fd9a5f303da 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -546,6 +546,56 @@ 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 super_block *sb;
+	struct inode *inode, *old_inode = NULL;
+	struct fuse_inode *fi;
+
+	inode = fuse_ilookup(fc, FUSE_ROOT_ID, NULL);
+	if (!inode)
+		return -ENOENT;
+
+	fm = get_fuse_mount(inode);
+	iput(inode);
+	if (!fm)
+		return -ENOENT;
+	sb = fm->sb;
+
+	spin_lock(&sb->s_inode_list_lock);
+	list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
+		spin_lock(&inode->i_lock);
+		if ((inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) ||
+		    !atomic_read(&inode->i_count)) {
+			spin_unlock(&inode->i_lock);
+			continue;
+		}
+
+		__iget(inode);
+		spin_unlock(&inode->i_lock);
+		spin_unlock(&sb->s_inode_list_lock);
+		iput(old_inode);
+
+		fi = get_fuse_inode(inode);
+		spin_lock(&fi->lock);
+		fi->attr_version = atomic64_inc_return(&fm->fc->attr_version);
+		spin_unlock(&fi->lock);
+		fuse_invalidate_attr(inode);
+		forget_all_cached_acls(inode);
+
+		old_inode = inode;
+		cond_resched();
+		spin_lock(&sb->s_inode_list_lock);
+	}
+	spin_unlock(&sb->s_inode_list_lock);
+	iput(old_inode);
+
+	shrink_dcache_sb(sb);
+
+	return 0;
+}
+
 int fuse_reverse_inval_inode(struct fuse_conn *fc, u64 nodeid,
 			     loff_t offset, loff_t len)
 {
@@ -554,6 +604,9 @@ 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 f1e99458e29e..e9e78292d107 100644
--- a/include/uapi/linux/fuse.h
+++ b/include/uapi/linux/fuse.h
@@ -658,6 +658,9 @@ 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