On 2022/01/04 4:03, Christoph Hellwig wrote:
> Make the legacy dev_t based autoloading optional and add a deprecation
> warning. This kind of autoloading has ceased to be useful about 20 years
> ago.
This is good for locking dependency simplification. But
>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> ---
> block/Kconfig | 11 +++++++++++
> block/bdev.c | 9 ++++++---
> block/genhd.c | 6 ++++++
> 3 files changed, 23 insertions(+), 3 deletions(-)
>
> diff --git a/block/Kconfig b/block/Kconfig
> index d5d4197b7ed2d..9cd8706faa7be 100644
> --- a/block/Kconfig
> +++ b/block/Kconfig
> @@ -26,6 +26,17 @@ menuconfig BLOCK
>
> if BLOCK
>
> +config BLOCK_LEGACY_AUTOLOAD
> + bool "Legacy autoloading support"
> + help
> + Enable loading modules and creating block device instances based on
> + accesses through their device special file. This is a historic Linux
> + feature and makes no sense in a udev world where device files are
> + created on demand.
> +
> + Say N here unless your boot broke without it, in which case you should
> + send a report to linux-block@xxxxxxxxxxxxxxx and your distribution.
I don't think the affected scope is limited to the boot process.
This change affects userspace programs which do not run in the boot process.
A program which do not use ioctl(LOOP_CTL_GET_FREE) would be possible.
Current:
----------
root@fuzz:~# ls -l /dev/loop*
crw-rw---- 1 root disk 10, 237 Jan 4 09:29 /dev/loop-control
root@fuzz:~# mknod /dev/loop0 b 7 0
root@fuzz:~# cat /dev/loop0
root@fuzz:~# echo $?
0
----------
With CONFIG_BLOCK_LEGACY_AUTOLOAD=n:
----------
root@fuzz:~# ls -l /dev/loop*
crw-rw---- 1 root disk 10, 237 Jan 4 09:33 /dev/loop-control
root@fuzz:~# mknod /dev/loop0 b 7 0
root@fuzz:~# cat /dev/loop0
cat: /dev/loop0: No such device or address
root@fuzz:~# echo $?
1
root@fuzz:~# losetup /dev/loop0 testfile
losetup: /dev/loop0: failed to set up loop device: No such device or address
----------
> +
> config BLK_RQ_ALLOC_TIME
> bool
>
> diff --git a/block/bdev.c b/block/bdev.c
> index 8bf93a19041b7..dd6fd5b807b30 100644
> --- a/block/bdev.c
> +++ b/block/bdev.c
> @@ -738,12 +738,15 @@ struct block_device *blkdev_get_no_open(dev_t dev)
> struct inode *inode;
>
> inode = ilookup(blockdev_superblock, dev);
> - if (!inode) {
> + if (!inode && IS_ENABLED(CONFIG_BLOCK_LEGACY_AUTOLOAD)) {
> blk_request_module(dev);
> inode = ilookup(blockdev_superblock, dev);
> - if (!inode)
> - return NULL;
> + if (inode)
> + pr_warn_ratelimited(
> +"block device autoloading is deprecated in will be removed in Linux 5.19\n");
s/deprecated in/deprecated; it/
> }
> + if (!inode)
> + return NULL;
>
> /* switch from the inode reference to a device mode one: */
> bdev = &BDEV_I(inode)->bdev;
