From: David Howells <dhowells@redhat.com>
Date: Wed, 18 Nov 2020 09:06:42 +0000
Subject: 9p: Copy local writes to the cache when writing to the server
Git-commit: 93c846143d8630d1fd465b69703b0f0021a543dc
Patch-mainline: v5.17-rc1
References: jsc#SES-1880

When writing to the server from v9fs_vfs_writepage(), copy the data to the
cache object too.

To make this possible, the cookie must have its active users count
incremented when the page is dirtied and kept incremented until we manage
to clean up all the pages.  This allows the writeback to take place after
the last file struct is released.

This is done by taking a use on the cookie in v9fs_set_page_dirty() if we
haven't already done so (controlled by the I_PINNING_FSCACHE_WB flag) and
dropping the pin in v9fs_write_inode() if __writeback_single_inode() clears
all the outstanding dirty pages (conveyed by the unpinned_fscache_wb flag
in the writeback_control struct).

Inode eviction must also clear the flag after truncating away all the
outstanding pages.

In the future this will be handled more gracefully by netfslib.

Changes
=======
ver #3:
 - Canonicalise the coherency data to make it endianness-independent.

ver #2:
 - Fix an unused-var warning due to CONFIG_9P_FSCACHE=n[1].

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Jeff Layton <jlayton@kernel.org>
Tested-by: Dominique Martinet <asmadeus@codewreck.org>
cc: Eric Van Hensbergen <ericvh@gmail.com>
cc: Latchesar Ionkov <lucho@ionkov.net>
cc: v9fs-developer@lists.sourceforge.net
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/163819667027.215744.13815687931204222995.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/163906978015.143852.10646669694345706328.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/163967180760.1823006.5831751873616248910.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/164021574522.640689.13849966660182529125.stgit@warthog.procyon.org.uk/ # v4
[adapted to use pages instead of folios]
Acked-by: Luis Henriques <lhenriques@suse.com>
---
 fs/9p/vfs_addr.c  |   47 ++++++++++++++++++++++++++++++++++++++++++++++-
 fs/9p/vfs_inode.c |    4 ++++
 fs/9p/vfs_super.c |    3 +++
 3 files changed, 53 insertions(+), 1 deletion(-)

--- a/fs/9p/vfs_addr.c
+++ b/fs/9p/vfs_addr.c
@@ -134,6 +134,8 @@ static void v9fs_vfs_readahead(struct re
 
 static int v9fs_release_page(struct page *page, gfp_t gfp)
 {
+	struct inode *inode = page->mapping->host;
+
 	if (PagePrivate(page))
 		return 0;
 #ifdef CONFIG_9P_FSCACHE
@@ -143,6 +145,7 @@ static int v9fs_release_page(struct page
 		wait_on_page_fscache(page);
 	}
 #endif
+	fscache_note_page_release(v9fs_inode_cookie(V9FS_I(inode)));
 	return 1;
 }
 
@@ -159,10 +162,25 @@ static void v9fs_invalidate_page(struct
 	wait_on_page_fscache(page);
 }
 
+static void v9fs_write_to_cache_done(void *priv, ssize_t transferred_or_error,
+				     bool was_async)
+{
+	struct v9fs_inode *v9inode = priv;
+	__le32 version;
+
+	if (IS_ERR_VALUE(transferred_or_error) &&
+	    transferred_or_error != -ENOBUFS) {
+		version = cpu_to_le32(v9inode->qid.version);
+		fscache_invalidate(v9fs_inode_cookie(v9inode), &version,
+				   i_size_read(&v9inode->vfs_inode), 0);
+	}
+}
+
 static int v9fs_vfs_writepage_locked(struct page *page)
 {
 	struct inode *inode = page->mapping->host;
 	struct v9fs_inode *v9inode = V9FS_I(inode);
+	struct fscache_cookie *cookie = v9fs_inode_cookie(v9inode);
 	loff_t start = page_offset(page);
 	loff_t size = i_size_read(inode);
 	struct iov_iter from;
@@ -178,10 +196,21 @@ static int v9fs_vfs_writepage_locked(str
 	/* We should have writeback_fid always set */
 	BUG_ON(!v9inode->writeback_fid);
 
+	wait_on_page_fscache(page);
 	set_page_writeback(page);
 
 	p9_client_write(v9inode->writeback_fid, start, &from, &err);
 
+	if (err == 0 &&
+	    fscache_cookie_enabled(cookie) &&
+	    test_bit(FSCACHE_COOKIE_IS_CACHING, &cookie->flags)) {
+		set_page_fscache(page);
+		fscache_write_to_cache(v9fs_inode_cookie(v9inode),
+				       page->mapping, start, len, size,
+				       v9fs_write_to_cache_done, v9inode,
+				       true);
+	}
+
 	end_page_writeback(page);
 	return err;
 }
@@ -293,6 +322,7 @@ static int v9fs_write_end(struct file *f
 {
 	loff_t last_pos = pos + copied;
 	struct inode *inode = page->mapping->host;
+	struct v9fs_inode *v9inode = V9FS_I(inode);
 
 	p9_debug(P9_DEBUG_VFS, "filp %p, mapping %p\n", filp, mapping);
 
@@ -312,6 +342,7 @@ static int v9fs_write_end(struct file *f
 	if (last_pos > inode->i_size) {
 		inode_add_bytes(inode, last_pos - inode->i_size);
 		i_size_write(inode, last_pos);
+		fscache_update_cookie(v9fs_inode_cookie(v9inode), NULL, &last_pos);
 	}
 	set_page_dirty(page);
 out:
@@ -321,11 +352,25 @@ out:
 	return copied;
 }
 
+#ifdef CONFIG_9P_FSCACHE
+/*
+ * Mark a page as having been made dirty and thus needing writeback.  We also
+ * need to pin the cache object to write back to.
+ */
+static int v9fs_set_page_dirty(struct page *page)
+{
+	struct v9fs_inode *v9inode = V9FS_I(page->mapping->host);
+
+	return fscache_set_page_dirty(page, v9fs_inode_cookie(v9inode));
+}
+#else
+#define v9fs_set_page_dirty __set_page_dirty_nobuffers
+#endif
 
 const struct address_space_operations v9fs_addr_operations = {
 	.readpage = v9fs_vfs_readpage,
 	.readahead = v9fs_vfs_readahead,
-	.set_page_dirty = __set_page_dirty_nobuffers,
+	.set_page_dirty = v9fs_set_page_dirty,
 	.writepage = v9fs_vfs_writepage,
 	.write_begin = v9fs_write_begin,
 	.write_end = v9fs_write_end,
--- a/fs/9p/vfs_inode.c
+++ b/fs/9p/vfs_inode.c
@@ -375,8 +375,12 @@ struct inode *v9fs_get_inode(struct supe
 void v9fs_evict_inode(struct inode *inode)
 {
 	struct v9fs_inode *v9inode = V9FS_I(inode);
+	__le32 version;
 
 	truncate_inode_pages_final(&inode->i_data);
+	version = cpu_to_le32(v9inode->qid.version);
+	fscache_clear_inode_writeback(v9fs_inode_cookie(v9inode), inode,
+				      &version);
 	clear_inode(inode);
 	filemap_fdatawrite(&inode->i_data);
 
--- a/fs/9p/vfs_super.c
+++ b/fs/9p/vfs_super.c
@@ -24,6 +24,7 @@
 #include <linux/slab.h>
 #include <linux/statfs.h>
 #include <linux/magic.h>
+#include <linux/fscache.h>
 #include <net/9p/9p.h>
 #include <net/9p/client.h>
 
@@ -307,6 +308,7 @@ static int v9fs_write_inode(struct inode
 		__mark_inode_dirty(inode, I_DIRTY_DATASYNC);
 		return ret;
 	}
+	fscache_unpin_writeback(wbc, v9fs_inode_cookie(v9inode));
 	return 0;
 }
 
@@ -330,6 +332,7 @@ static int v9fs_write_inode_dotl(struct
 		__mark_inode_dirty(inode, I_DIRTY_DATASYNC);
 		return ret;
 	}
+	fscache_unpin_writeback(wbc, v9fs_inode_cookie(v9inode));
 	return 0;
 }