linux-kernel - [PATCH bpf-next 1/2] libfs: support RENAME_EXCHANGE in simple

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Message-Id: <20211020082956.8359-2-lmb@cloudflare.com>
Date:   Wed, 20 Oct 2021 09:29:55 +0100
From:   Lorenz Bauer <lmb@...udflare.com>
To:     Alexander Viro <viro@...iv.linux.org.uk>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>
Cc:     kernel-team@...udflare.com, Lorenz Bauer <lmb@...udflare.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, bpf@...r.kernel.org
Subject: [PATCH bpf-next 1/2] libfs: support RENAME_EXCHANGE in simple_rename()

Allow atomic exchange via RENAME_EXCHANGE when using simple_rename.
This affects binderfs, ramfs, hubetlbfs and bpffs. There isn't much
to do except update the various *time fields.

Signed-off-by: Lorenz Bauer <lmb@...udflare.com>
---
 fs/libfs.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/fs/libfs.c b/fs/libfs.c
index 51b4de3b3447..93c03d593749 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -455,9 +455,12 @@ int simple_rename(struct user_namespace *mnt_userns, struct inode *old_dir,
 	struct inode *inode = d_inode(old_dentry);
 	int they_are_dirs = d_is_dir(old_dentry);
 
-	if (flags & ~RENAME_NOREPLACE)
+	if (flags & ~(RENAME_NOREPLACE | RENAME_EXCHANGE))
 		return -EINVAL;
 
+	if (flags & RENAME_EXCHANGE)
+		goto done;
+
 	if (!simple_empty(new_dentry))
 		return -ENOTEMPTY;
 
@@ -472,6 +475,7 @@ int simple_rename(struct user_namespace *mnt_userns, struct inode *old_dir,
 		inc_nlink(new_dir);
 	}
 
+done:
 	old_dir->i_ctime = old_dir->i_mtime = new_dir->i_ctime =
 		new_dir->i_mtime = inode->i_ctime = current_time(old_dir);
 
-- 
2.30.2