Re: [PATCH RFC] introduce ioctl to completely invalidate page cache

This patch introduces a new ioctl called BLKFLUSHBUFS2, which is pretty
similar to BLKFLUSHBUFS except that is also invalidates the page cache.
This allows for a complete invalidation of the cached data of a
particular block device, which might be useful for cases like
synchronising the caches of an iSCSI block device used by multiple
hosts.

Signed-off-by: Thanos Makatos <redacted>
---
 block/compat_ioctl.c    |    1 +
 block/ioctl.c           |   13 +++++++++++--
 include/uapi/linux/fs.h |    1 +
 3 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/block/compat_ioctl.c b/block/compat_ioctl.c
index 18b282c..672388ab 100644
--- a/block/compat_ioctl.c
+++ b/block/compat_ioctl.c

@@ -688,6 +688,7 @@ long compat_blkdev_ioctl(struct file *file, unsigned cmd, unsigned long arg)
 	case BLKDISCARDZEROES:
 		return compat_put_uint(arg, bdev_discard_zeroes_data(bdev));
 	case BLKFLSBUF:
+	case BLKFLSBUF2:
 	case BLKROSET:
 	case BLKDISCARD:
 	case BLKSECDISCARD:

diff --git a/block/ioctl.c b/block/ioctl.c
index d6cda81..0c427a7 100644
--- a/block/ioctl.c
+++ b/block/ioctl.c

@@ -268,6 +268,12 @@ static inline int is_unrecognized_ioctl(int ret)
 		ret == -ENOIOCTLCMD;
 }
 
+static void flush_buffer_cache(struct block_device *bdev)
+{
+	fsync_bdev(bdev);
+	invalidate_bdev(bdev);
+}
+
 /*
  * always keep this in sync with compat_blkdev_ioctl()
  */

@@ -282,6 +288,7 @@ int blkdev_ioctl(struct block_device *bdev, fmode_t mode, unsigned cmd,
 
 	switch(cmd) {
 	case BLKFLSBUF:
+	case BLKFLSBUF2:
 		if (!capable(CAP_SYS_ADMIN))
 			return -EACCES;
 

@@ -289,8 +296,10 @@ int blkdev_ioctl(struct block_device *bdev, fmode_t mode, unsigned cmd,
 		if (!is_unrecognized_ioctl(ret))
 			return ret;
 
-		fsync_bdev(bdev);
-		invalidate_bdev(bdev);
+		flush_buffer_cache(bdev);
+		if (BLKFLSBUF2 == cmd)
+			return invalidate_inode_pages2(
+					bdev->bd_inode->i_mapping);
 		return 0;