linux-kernel - [PATCH 3/5] vfs: Allow fsinfo() to query what's in an fs

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Date:   Fri, 21 Sep 2018 17:38:11 +0100
From:   David Howells <dhowells@...hat.com>
To:     viro@...iv.linux.org.uk
Cc:     torvalds@...ux-foundation.org, dhowells@...hat.com,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        mszeredi@...hat.com
Subject: [PATCH 3/5] vfs: Allow fsinfo() to query what's in an fs_context
 [ver #12]

Allow fsinfo() to be used to query the filesystem attached to an fs_context
once a superblock has been created or if it comes from fspick().

This is done with something like:

	fd = fsopen("ext4", 0);
	...
	fsconfig(fd, fsconfig_cmd_create, ...);
	fsinfo(fd, NULL, ...);

Signed-off-by: David Howells <dhowells@...hat.com>
---

 fs/statfs.c |   32 ++++++++++++++++++++++++++++++--
 1 file changed, 30 insertions(+), 2 deletions(-)

diff --git a/fs/statfs.c b/fs/statfs.c
index f3cf8aa42a3d..790e21367d70 100644
--- a/fs/statfs.c
+++ b/fs/statfs.c
@@ -636,7 +636,8 @@ int vfs_fsinfo(struct path *path, struct fsinfo_kparams *params)
 		return ret;
 
 	if (params->request == FSINFO_ATTR_IDS &&
-	    params->buffer) {
+	    params->buffer &&
+	    path->mnt) {
 		struct fsinfo_ids *p = params->buffer;
 
 		p->f_flags |= flags_by_mnt(path->mnt->mnt_flags);
@@ -677,13 +678,40 @@ static int vfs_fsinfo_path(int dfd, const char __user *filename,
 	return ret;
 }
 
+static int vfs_fsinfo_fscontext(struct fs_context *fc,
+				struct fsinfo_kparams *params)
+{
+	int ret;
+
+	if (fc->ops == &legacy_fs_context_ops)
+		return -EOPNOTSUPP;
+
+	ret = mutex_lock_interruptible(&fc->uapi_mutex);
+	if (ret < 0)
+		return ret;
+
+	ret = -EIO;
+	if (fc->root) {
+		struct path path = { .dentry = fc->root };
+
+		ret = vfs_fsinfo(&path, params);
+	}
+
+	mutex_unlock(&fc->uapi_mutex);
+	return ret;
+}
+
 static int vfs_fsinfo_fd(unsigned int fd, struct fsinfo_kparams *params)
 {
 	struct fd f = fdget_raw(fd);
 	int ret = -EBADF;
 
 	if (f.file) {
-		ret = vfs_fsinfo(&f.file->f_path, params);
+		if (f.file->f_op == &fscontext_fops)
+			ret = vfs_fsinfo_fscontext(f.file->private_data,
+						   params);
+		else
+			ret = vfs_fsinfo(&f.file->f_path, params);
 		fdput(f);
 	}
 	return ret;