block: Add vfs_msg() interface

In preparation of moving DAX capability checks to the block layer
from filesystem code, add a VFS message interface that aligns with
filesystem's message format.

For instance, a vfs_msg() message followed by XFS messages in case
of a dax mount error may look like:

  VFS (pmem0p1): error: unaligned partition for dax
  XFS (pmem0p1): DAX unsupported by block device. Turning off DAX.
  XFS (pmem0p1): Mounting V5 Filesystem
   :

vfs_msg() is largely based on ext4_msg().

Signed-off-by: Toshi Kani <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Cc: Alexander Viro <[email protected]>
Cc: Jens Axboe <[email protected]>
Cc: "Theodore Ts'o" <[email protected]>
Cc: Andreas Dilger <[email protected]>
Cc: Jan Kara <[email protected]>
Cc: Dave Chinner <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: Ross Zwisler <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Boaz Harrosh <[email protected]>
Signed-off-by: Vishal Verma <[email protected]>

Author: toshikani

fs/block_dev.c

@@ -50,6 +50,18 @@ struct block_device *I_BDEV(struct inode *inode)
 }
 EXPORT_SYMBOL(I_BDEV);
 
+void __vfs_msg(struct super_block *sb, const char *prefix, const char *fmt, ...)
+{
+	struct va_format vaf;
+	va_list args;
+
+	va_start(args, fmt);
+	vaf.fmt = fmt;
+	vaf.va = &args;
+	printk_ratelimited("%sVFS (%s): %pV\n", prefix, sb->s_id, &vaf);
+	va_end(args);
+}
+
 static void bdev_write_inode(struct block_device *bdev)
 {
 	struct inode *inode = bdev->bd_inode;

include/linux/blkdev.h

@@ -767,6 +767,17 @@ static inline void rq_flush_dcache_pages(struct request *rq)
 }
 #endif
 
+#ifdef CONFIG_PRINTK
+#define vfs_msg(sb, level, fmt, ...)				\
+	__vfs_msg(sb, level, fmt, ##__VA_ARGS__)
+#else
+#define vfs_msg(sb, level, fmt, ...)				\
+do {								\
+	no_printk(fmt, ##__VA_ARGS__);				\
+	__vfs_msg(sb, "", " ");					\
+} while (0)
+#endif
+
 extern int blk_register_queue(struct gendisk *disk);
 extern void blk_unregister_queue(struct gendisk *disk);
 extern blk_qc_t generic_make_request(struct bio *bio);