ubi: fastmap: Add fastmap control support for 'UBI_IOCATT' ioctl

mainline inclusion
from mainline-v6.1-rc1
commit 669d2044
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5WQRM
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=669d204469c46e91d99da24914130f78277a71d3

--------------------------------

[1] suggests that fastmap is suitable for large flash devices. Module
parameter 'fm_autoconvert' is a coarse grained switch to enable all
ubi devices to generate fastmap, which may turn on fastmap even for
small flash devices.

This patch imports a new field 'disable_fm' in struct 'ubi_attach_req'
to support following situations by ioctl 'UBI_IOCATT'.
 [old functions]
 A. Disable 'fm_autoconvert': Disbable fastmap for all ubi devices
 B. Enable 'fm_autoconvert': Enable fastmap for all ubi devices
 [new function]
 C. Enable 'fm_autoconvert', set 'disable_fm' for given device: Don't
    create new fastmap and do full scan (existed fastmap will be
    destroyed) for the given ubi device.

A simple test case in [2].

[1] http://www.linux-mtd.infradead.org/doc/ubi.html#L_fastmap
[2] https://bugzilla.kernel.org/show_bug.cgi?id=216278



Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
Reviewed-by: Zhihao Cheng <chengzhihao1@huawei.com>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>