shmem: allow reporting fanotify events with file handles on tmpfs

mainline inclusion
from mainline-5.13-rc1
commit 59cda49e
category: feature
bugzilla: 187162, https://gitee.com/openeuler/kernel/issues/I5FYKV
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=59cda49ecf6c9a32fae4942420701b6e087204f6

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Since kernel v5.1, fanotify_init(2) supports the flag FAN_REPORT_FID
for identifying objects using file handle and fsid in events.

fanotify_mark(2) fails with -ENODEV when trying to set a mark on
filesystems that report null f_fsid in stasfs(2).

Use the digest of uuid as f_fsid for tmpfs to uniquely identify tmpfs
objects as best as possible and allow setting an fanotify mark that
reports events with file handles on tmpfs.

Link: https://lore.kernel.org/r/20210322173944.449469-3-amir73il@gmail.com


Acked-by: Hugh Dickins <hughd@google.com>
Reviewed-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: chengzhihao <chengzhihao1@huawei.com>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>