[PATCH 6.12.y 2/2] 9p: Fix v9fs_issue_write() to update i_size and remote_i_size

[Sasha Levin <sashal@kernel.org>]

From: David Howells <dhowells@redhat.com>

[ Upstream commit c60ae98c5aa64021751b38ab1313b19d620bf640 ]

Fix v9fs_issue_write() to update i_size and remote_i_size to the new size
of the server file if we made it larger, using the start fpos and the count
returned by p9_client_write() to calculate the new minimum file size.

This assumes that if the 9P server makes a short write (say it hits
ENOSPC), a reduced count is returned.

Fixes: 5fb70e7275a6 ("netfs, 9p: Implement helpers for new write code")
Reported-by: Michael Mulqueen <mike@method-b.uk>
Closes: https://lore.kernel.org/r/fbb9e395-1e07-4212-8f70-23f3cd498074@method-b.uk/
Cc: stable@vger.kernel.org
Signed-off-by: David Howells <dhowells@redhat.com>
Message-ID: <2226525.1789118704@warthog.procyon.org.uk>
Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>
[ replaced unavailable netfs_write_sizes() with i_size_write() and direct remote_i_size updates under inode->i_lock. ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/9p/vfs_addr.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/fs/9p/vfs_addr.c b/fs/9p/vfs_addr.c
index d6107ac50e882..5bf1e5caaa623 100644
--- a/fs/9p/vfs_addr.c
+++ b/fs/9p/vfs_addr.c
@@ -54,9 +54,21 @@ static void v9fs_begin_writeback(struct netfs_io_request *wreq)
 static void v9fs_issue_write(struct netfs_io_subrequest *subreq)
 {
 	struct p9_fid *fid = subreq->rreq->netfs_priv;
+	struct inode *inode = subreq->rreq->inode;
+	struct netfs_inode *ictx = netfs_inode(inode);
 	int err, len;
 
 	len = p9_client_write(fid, subreq->start, &subreq->io_iter, &err);
+	if (len > 0) {
+		unsigned long long end = subreq->start + len;
+
+		spin_lock(&inode->i_lock);
+		if (end > i_size_read(inode))
+			i_size_write(inode, end);
+		if (end > ictx->remote_i_size)
+			ictx->remote_i_size = end;
+		spin_unlock(&inode->i_lock);
+	}
 	netfs_write_subrequest_terminated(subreq, len ?: err, false);
 }
 
-- 
2.53.0