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Yu Kuai e4c4871a73 nbd: fix max value for 'first_minor' 
commit b1a811633f ("block: nbd: add sanity check for first_minor")
checks that 'first_minor' should not be greater than 0xff, which is
wrong. Whitout the commit, the details that when user pass 0x100000,
it ends up create sysfs dir "/sys/block/43:0" are as follows:

nbd_dev_add
 disk->first_minor = index << part_shift
  -> default part_shift is 5, first_minor is 0x2000000
  device_add_disk
   ddev->devt = MKDEV(disk->major, disk->first_minor)
    -> (0x2b << 20) | (0x2000000) = 0x2b00000
   device_add
    device_create_sys_dev_entry
	 format_dev_t
	  sprintf(buffer, "%u:%u", MAJOR(dev), MINOR(dev));
	   -> got 43:0
	  sysfs_create_link -> /sys/block/43:0

By the way, with the wrong fix, when part_shift is the default value,
only 8 ndb devices can be created since 8 << 5 is greater than 0xff.

Since the max bits for 'first_minor' should be the same as what
MKDEV() does, which is 20. Change the upper bound of 'first_minor'
from 0xff to 0xfffff.

Fixes: b1a811633f ("block: nbd: add sanity check for first_minor")
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Link: https://lore.kernel.org/r/20211102015237.2309763-2-yebin10@huawei.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
History 2021-11-02 10:50:27 -06:00
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README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.