From:   Jeffle Xu <jefflexu@linux.alibaba.com>
To:     dhowells@redhat.com, linux-cachefs@redhat.com, xiang@kernel.org,
        chao@kernel.org, linux-erofs@lists.ozlabs.org
Cc:     linux-fsdevel@vger.kernel.org, joseph.qi@linux.alibaba.com,
        bo.liu@linux.alibaba.com, tao.peng@linux.alibaba.com,
        gerry@linux.alibaba.com, eguan@linux.alibaba.com,
        linux-kernel@vger.kernel.org
Subject: [PATCH v1 01/23] cachefiles: add cachefiles_demand devnode
Date:   Mon, 27 Dec 2021 20:54:22 +0800
Message-Id: <20211227125444.21187-2-jefflexu@linux.alibaba.com>
In-Reply-To: <20211227125444.21187-1-jefflexu@linux.alibaba.com>
References: <20211227125444.21187-1-jefflexu@linux.alibaba.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

fscache/cachefiles used to serve as a local cache for remote fs. The
following patches will introduce a new use case, in which local
read-only fs could implement demand reading with fscache. By then the
user daemon needs to read and poll on the devnode, and thus the original
cachefiles devnode can't be reused in this case.

Thus create a new devnode specifically for the new mode. The following
patches will add more file_operations.

Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
---
 fs/cachefiles/daemon.c   |  8 ++++++++
 fs/cachefiles/internal.h |  1 +
 fs/cachefiles/main.c     | 12 ++++++++++++
 3 files changed, 21 insertions(+)

diff --git a/fs/cachefiles/daemon.c b/fs/cachefiles/daemon.c
index 40a792421fc1..871f1e0f423d 100644
--- a/fs/cachefiles/daemon.c
+++ b/fs/cachefiles/daemon.c
@@ -56,6 +56,14 @@ const struct file_operations cachefiles_daemon_fops = {
 	.llseek		= noop_llseek,
 };
 
+const struct file_operations cachefiles_demand_fops = {
+	.owner		= THIS_MODULE,
+	.open		= cachefiles_daemon_open,
+	.release	= cachefiles_daemon_release,
+	.write		= cachefiles_daemon_write,
+	.llseek		= noop_llseek,
+};
+
 struct cachefiles_daemon_cmd {
 	char name[8];
 	int (*handler)(struct cachefiles_cache *cache, char *args);
diff --git a/fs/cachefiles/internal.h b/fs/cachefiles/internal.h
index 421423819d63..e0ed811d628d 100644
--- a/fs/cachefiles/internal.h
+++ b/fs/cachefiles/internal.h
@@ -145,6 +145,7 @@ extern int cachefiles_has_space(struct cachefiles_cache *cache,
  * daemon.c
  */
 extern const struct file_operations cachefiles_daemon_fops;
+extern const struct file_operations cachefiles_demand_fops;
 
 /*
  * error_inject.c
diff --git a/fs/cachefiles/main.c b/fs/cachefiles/main.c
index 3f369c6f816d..0a423274d283 100644
--- a/fs/cachefiles/main.c
+++ b/fs/cachefiles/main.c
@@ -39,6 +39,12 @@ static struct miscdevice cachefiles_dev = {
 	.fops	= &cachefiles_daemon_fops,
 };
 
+static struct miscdevice cachefiles_demand_dev = {
+	.minor	= MISC_DYNAMIC_MINOR,
+	.name	= "cachefiles_demand",
+	.fops	= &cachefiles_demand_fops,
+};
+
 /*
  * initialise the fs caching module
  */
@@ -52,6 +58,9 @@ static int __init cachefiles_init(void)
 	ret = misc_register(&cachefiles_dev);
 	if (ret < 0)
 		goto error_dev;
+	ret = misc_register(&cachefiles_demand_dev);
+	if (ret < 0)
+		goto error_demand_dev;
 
 	/* create an object jar */
 	ret = -ENOMEM;
@@ -68,6 +77,8 @@ static int __init cachefiles_init(void)
 	return 0;
 
 error_object_jar:
+	misc_deregister(&cachefiles_demand_dev);
+error_demand_dev:
 	misc_deregister(&cachefiles_dev);
 error_dev:
 	cachefiles_unregister_error_injection();
@@ -86,6 +97,7 @@ static void __exit cachefiles_exit(void)
 	pr_info("Unloading\n");
 
 	kmem_cache_destroy(cachefiles_object_jar);
+	misc_deregister(&cachefiles_demand_dev);
 	misc_deregister(&cachefiles_dev);
 	cachefiles_unregister_error_injection();
 }
-- 
2.27.0