[Devel] [PATCH RHEL7 COMMIT] fuse kio: minimal noop engine skeleton

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-693.17.1.vz7.45.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-693.17.1.vz7.43.7
------>
commit e00e6b130677c3ed9a773a9fd40ad4293224de25
Author: Dmitry Monakhov <dmonakhov at openvz.org>
Date:   Mon Feb 19 14:16:28 2018 +0300

    fuse kio: minimal noop engine skeleton
    
    https://jira.sw.ru/browse/PSBM-80680
    Signed-off-by: Dmitry Monakhov <dmonakhov at openvz.org>
---
 fs/fuse/Kconfig        |   8 +++
 fs/fuse/Makefile       |   3 ++
 fs/fuse/kio/kio_noop.c | 130 +++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 141 insertions(+)

diff --git a/fs/fuse/Kconfig b/fs/fuse/Kconfig
index 1b2f6c2c3aaf..fcbb5a565fc6 100644
--- a/fs/fuse/Kconfig
+++ b/fs/fuse/Kconfig
@@ -25,3 +25,11 @@ config CUSE
 
 	  If you want to develop or use a userspace character device
 	  based on CUSE, answer Y or M.
+
+config FUSE_KIO_NOOP
+	tristate "Enable kdirect noop io engine"
+	depends on FUSE_FS
+	help
+	  This FUSE extension allows to handle io requests directly inside kernel
+
+	  This is for kdirect io feature debugging only, answer Y or M.
diff --git a/fs/fuse/Makefile b/fs/fuse/Makefile
index e95eeb445e58..4a250c083f0d 100644
--- a/fs/fuse/Makefile
+++ b/fs/fuse/Makefile
@@ -5,4 +5,7 @@
 obj-$(CONFIG_FUSE_FS) += fuse.o
 obj-$(CONFIG_CUSE) += cuse.o
 
+obj-$(CONFIG_FUSE_KIO_NOOP)	+= fuse_kio_noop.o
+fuse_kio_noop-objs := kio/kio_noop.o
+
 fuse-objs := dev.o dir.o file.o inode.o control.o
diff --git a/fs/fuse/kio/kio_noop.c b/fs/fuse/kio/kio_noop.c
new file mode 100644
index 000000000000..914ed542e762
--- /dev/null
+++ b/fs/fuse/kio/kio_noop.c
@@ -0,0 +1,130 @@
+#include <linux/module.h>
+#include <linux/errno.h>
+#include <linux/sched.h>
+#include <linux/kernel.h>
+#include <linux/fs.h>
+#include <linux/slab.h>
+#include <linux/printk.h>
+
+#include "../fuse_i.h"
+
+static struct fuse_kio_ops noop_ops;
+static struct kmem_cache *noop_req_cachep;
+
+/* Conn hooks */
+
+static int noop_probe(struct fuse_conn *fc, char *name)
+{
+	if (!strncmp(name, noop_ops.name, FUSE_KIO_NAME))
+		return 1;
+
+	return 0;
+}
+
+static int noop_conn_init(struct fuse_conn *fc)
+{
+	/* Just for sanity checks */
+	fc->kio.ctx = noop_req_cachep;
+	pr_debug("fuse_kio_noop: init");
+
+	/*This one is mandatary */
+	fuse_set_initialized(fc);
+	wake_up_all(&fc->blocked_waitq);
+
+	return 0;
+}
+
+static void noop_conn_fini(struct fuse_conn *fc)
+{
+	BUG_ON(fc->kio.ctx != noop_req_cachep);
+	pr_debug("fuse_kio_noop: fini");
+
+}
+
+static void noop_conn_abort(struct fuse_conn *fc)
+{
+	BUG_ON(fc->kio.ctx != noop_req_cachep);
+	pr_debug("fuse_kio_noop: abort");
+}
+
+/* Request hooks */
+static struct fuse_req *noop_req_alloc(struct fuse_conn *fc, unsigned npages,
+				       gfp_t flags)
+{
+	return fuse_generic_request_alloc(fc, noop_req_cachep, npages, flags);
+}
+
+static int noop_req_send(struct fuse_conn *fc, struct fuse_req *req, bool bg,
+			 bool locked)
+{
+	/* Do not intercept request for unconnected channel */
+	if (!fc->initialized)
+		return 1;
+
+	BUG_ON(fc->kio.ctx != noop_req_cachep);
+	BUG_ON(req->cache != noop_req_cachep);
+
+	/* fall back to generic fuse io-flow */
+	return 1;
+}
+
+/* Optional inode scope hooks
+static int noop_file_open(struct fuse_conn *fc, struct file *file,
+			  struct inode *inode)
+{
+	return 0;
+}
+
+static void noop_inode_release(struct fuse_inode *fi)
+{
+}
+*/
+
+static struct fuse_kio_ops noop_ops = {
+	.name		= "noop",
+	.owner		= THIS_MODULE,
+	.probe		= noop_probe,
+
+	.conn_init	= noop_conn_init,
+	.conn_fini	= noop_conn_fini,
+	.conn_abort	= noop_conn_abort,
+	.req_alloc	= noop_req_alloc,
+	.req_send	= noop_req_send,
+	/* Optional inode state hooks
+	 *.file_open	= noop_file_open,
+	 *.inode_release= noop_inode_release,
+	 */
+};
+
+static int __init kio_noop_mod_init(void)
+{
+	int err;
+
+	noop_req_cachep = kmem_cache_create("noop_fuse_request",
+					    sizeof(struct fuse_req),
+					    0, 0, NULL);
+	if (!noop_req_cachep)
+		return -ENOMEM;
+
+	err = -EINVAL;
+	if (fuse_register_kio(&noop_ops))
+		goto free_cache;
+
+	return 0;
+
+free_cache:
+	kmem_cache_destroy(noop_req_cachep);
+	return err;
+}
+
+static void __exit kio_noop_mod_exit(void)
+{
+	fuse_unregister_kio(&noop_ops);
+	kmem_cache_destroy(noop_req_cachep);
+}
+
+module_init(kio_noop_mod_init);
+module_exit(kio_noop_mod_exit);
+
+MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR("Virtuozzo <devel at openvz.org>");