[RFC PATCH bpf-next v2 02/17] bpf: create /sys/kernel/bpfdump mount file system

Yonghong Song
2020-04-15T19:31:17Z

This patch creates a mount point "bpfdump" under
/sys/kernel. The file system has a single user
mode, i.e., all mount points will be identical.

The magic number I picked for the new file system
is "dump".

Signed-off-by: Yonghong Song <yhs@fb.com>
---
include/uapi/linux/magic.h | 1 +
kernel/bpf/Makefile | 1 +
kernel/bpf/dump.c | 79 ++++++++++++++++++++++++++++++++++++++
3 files changed, 81 insertions(+)
create mode 100644 kernel/bpf/dump.c

diff --git a/include/uapi/linux/magic.h b/include/uapi/linux/magic.h
index d78064007b17..4ce3d8882315 100644
--- a/include/uapi/linux/magic.h
+++ b/include/uapi/linux/magic.h
@@ -88,6 +88,7 @@
#define BPF_FS_MAGIC 0xcafe4a11
#define AAFS_MAGIC 0x5a3c69f0
#define ZONEFS_MAGIC 0x5a4f4653
+#define DUMPFS_MAGIC 0x64756d70

/* Since UDF 2.01 is ISO 13346 based... */
#define UDF_SUPER_MAGIC 0x15013346
diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile
index f2d7be596966..4a1376ab2bea 100644
--- a/kernel/bpf/Makefile
+++ b/kernel/bpf/Makefile
@@ -26,6 +26,7 @@ obj-$(CONFIG_BPF_SYSCALL) += reuseport_array.o
endif
ifeq ($(CONFIG_SYSFS),y)
obj-$(CONFIG_DEBUG_INFO_BTF) += sysfs_btf.o
+obj-$(CONFIG_BPF_SYSCALL) += dump.o
endif
ifeq ($(CONFIG_BPF_JIT),y)
obj-$(CONFIG_BPF_SYSCALL) += bpf_struct_ops.o
diff --git a/kernel/bpf/dump.c b/kernel/bpf/dump.c
new file mode 100644
index 000000000000..e0c33486e0e7
--- /dev/null
+++ b/kernel/bpf/dump.c
@@ -0,0 +1,79 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright (c) 2020 Facebook */
+
+#include <linux/init.h>
+#include <linux/magic.h>
+#include <linux/mount.h>
+#include <linux/anon_inodes.h>
+#include <linux/namei.h>
+#include <linux/fs.h>
+#include <linux/fs_context.h>
+#include <linux/fs_parser.h>
+#include <linux/filter.h>
+#include <linux/bpf.h>
+
+static void bpfdump_free_inode(struct inode *inode)
+{
+ kfree(inode->i_private);
+ free_inode_nonrcu(inode);
+}
+
+static const struct super_operations bpfdump_super_operations = {
+ .statfs = simple_statfs,
+ .free_inode = bpfdump_free_inode,
+};
+
+static int bpfdump_fill_super(struct super_block *sb, struct fs_context *fc)
+{
+ static const struct tree_descr files[] = { { "" } };
+ int err;
+
+ err = simple_fill_super(sb, DUMPFS_MAGIC, files);
+ if (err)
+ return err;
+
+ sb->s_op = &bpfdump_super_operations;
+ return 0;
+}
+
+static int bpfdump_get_tree(struct fs_context *fc)
+{
+ return get_tree_single(fc, bpfdump_fill_super);
+}
+
+static const struct fs_context_operations bpfdump_context_ops = {
+ .get_tree = bpfdump_get_tree,
+};
+
+static int bpfdump_init_fs_context(struct fs_context *fc)
+{
+ fc->ops = &bpfdump_context_ops;
+ return 0;
+}
+
+static struct file_system_type fs_type = {
+ .owner = THIS_MODULE,
+ .name = "bpfdump",
+ .init_fs_context = bpfdump_init_fs_context,
+ .kill_sb = kill_litter_super,
+};
+
+static int __init bpfdump_init(void)
+{
+ int ret;
+
+ ret = sysfs_create_mount_point(kernel_kobj, "bpfdump");
+ if (ret)
+ return ret;
+
+ ret = register_filesystem(&fs_type);
+ if (ret)
+ goto remove_mount;
+
+ return 0;
+
+remove_mount:
+ sysfs_remove_mount_point(kernel_kobj, "bpfdump");
+ return ret;
+}
+core_initcall(bpfdump_init);
--
2.24.1