On Thu, 18 Aug 2011, Randy Dunlap wrote:

On Thu, 18 Aug 2011 14:18:22 +0200 Lukas Czerner wrote:

quoted

 fs/Makefile        |    2 +-
 fs/netlink.c       |  107 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/fs.h |   11 +++++
 3 files changed, 119 insertions(+), 1 deletions(-)
 create mode 100644 fs/netlink.c

Hi,

Does this build OK when CONFIG_NET is not enabled?

Good point :), it does not. I'll fix that once I have more comments.

and also for kernels that do not have CONFIG_NET enabled:  are these
new netlink messages basically duplicates of printk() calls that are
already there and will remain there?

No they are not. There is not a single printk I am duplicating right
now.

Thanks!
-Lukas

Thanks.

quoted

diff --git a/fs/Makefile b/fs/Makefile
index afc1096..7e9c61f 100644
--- a/fs/Makefile
+++ b/fs/Makefile

@@ -11,7 +11,7 @@ obj-y :=	open.o read_write.o file_table.o super.o \
 		attr.o bad_inode.o file.o filesystems.o namespace.o \
 		seq_file.o xattr.o libfs.o fs-writeback.o \
 		pnode.o drop_caches.o splice.o sync.o utimes.o \
-		stack.o fs_struct.o statfs.o
+		stack.o fs_struct.o statfs.o netlink.o
 
 ifeq ($(CONFIG_BLOCK),y)
 obj-y +=	buffer.o bio.o block_dev.o direct-io.o mpage.o ioprio.o

diff --git a/fs/netlink.c b/fs/netlink.c
new file mode 100644
index 0000000..15c44a1
--- /dev/null
+++ b/fs/netlink.c

@@ -0,0 +1,107 @@
+#include <linux/fs.h>
+#include <linux/cred.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include <net/netlink.h>
+#include <net/genetlink.h>
+
+enum {
+	FS_NL_A_UNSPEC,
+	FS_NL_A_WARNING,
+	FS_NL_A_DEV_MAJOR,
+	FS_NL_A_DEV_MINOR,
+	FS_NL_A_CAUSED_ID,
+	__FS_NL_A_MAX,
+};
+#define FS_NL_A_MAX (__FS_NL_A_MAX - 1)
+
+enum {
+	FS_NL_C_UNSPEC,
+	FS_NL_C_WARNING,
+	__FS_NL_C_MAX,
+};
+#define FS_NL_C_MAX (__FS_NL_C_MAX - 1)
+
+
+static struct genl_family fs_genl_family = {
+	.id = GENL_ID_GENERATE,
+	.hdrsize = 0,
+	.name = "FS_MSG",
+	.version = 1,
+	.maxattr = FS_NL_A_MAX,
+};
+static int registered;
+
+/**
+ * fs_nl_send_warning - Send warning from file system to userspace
+ * @dev: The device on which the fs is mounted
+ * @warntype: The type of the warning
+ *
+ * This can be used by file systems to send a warning message to the
+ * userspace.
+ */
+
+void fs_nl_send_warning(dev_t dev, unsigned int warntype)
+{
+	static atomic_t seq;
+	struct sk_buff *skb;
+	void *msg_head;
+	int ret;
+	int msg_size = nla_total_size(sizeof(u64)) +
+			3 * nla_total_size(sizeof(u32));
+
+	/* We have to allocate using GFP_NOFS as we are called from a
+	 * filesystem performing write and thus further recursion into
+	 * the fs to free some data could cause deadlocks. */
+	skb = genlmsg_new(msg_size, GFP_NOFS);
+	if (!skb) {
+		printk(KERN_ERR
+		  "VFS: Not enough memory to send fs warning.\n");
+		return;
+	}
+	msg_head = genlmsg_put(skb, 0, atomic_add_return(1, &seq),
+			&fs_genl_family, 0, FS_NL_C_WARNING);
+	if (!msg_head) {
+		printk(KERN_ERR
+		  "VFS: Cannot store netlink header in fs warning.\n");
+		goto err_out;
+	}
+	ret = nla_put_u32(skb, FS_NL_A_WARNING, warntype);
+	if (ret)
+		goto attr_err_out;
+	ret = nla_put_u32(skb, FS_NL_A_DEV_MAJOR, MAJOR(dev));
+	if (ret)
+		goto attr_err_out;
+	ret = nla_put_u32(skb, FS_NL_A_DEV_MINOR, MINOR(dev));
+	if (ret)
+		goto attr_err_out;
+	ret = nla_put_u64(skb, FS_NL_A_CAUSED_ID, current_uid());
+	if (ret)
+		goto attr_err_out;
+	genlmsg_end(skb, msg_head);
+	genlmsg_multicast(skb, 0, fs_genl_family.id, GFP_NOFS);
+	return;
+attr_err_out:
+	printk(KERN_ERR "VFS: Not enough space to compose "
+			"fs netlink message!\n");
+err_out:
+	kfree_skb(skb);
+}
+EXPORT_SYMBOL(fs_nl_send_warning);
+
+void init_fs_nl_family(void)
+{
+	if (registered)
+		return;
+
+	if (genl_register_family(&fs_genl_family) != 0) {
+		printk(KERN_ERR
+		       "VFS: Failed to create fs netlink interface.\n");
+		return;
+	}
+	registered = 1;
+}
+EXPORT_SYMBOL(init_fs_nl_family);

---
~Randy
*** Remember to use Documentation/SubmitChecklist when testing your code ***

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