docs: filesystems: convert inotify.txt to ReST

- Add a SPDX header;
- Add a document title;
- Adjust document title;
- Fix list markups;
- Some whitespace fixes and new line breaks;
- Add it to filesystems/index.rst.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Acked-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/8f846843ecf1914988feb4d001e3a53d27dc1a65.1581955849.git.mchehab+huawei@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/filesystems/index.rst

@@ -70,6 +70,7 @@ Documentation for filesystem implementations.
    hfs
    hfsplus
    hpfs
+   inotify
    fuse
    overlayfs
    virtiofs

Documentation/filesystems/inotify.rst

@@ -1,27 +1,36 @@
-				   inotify
-	    a powerful yet simple file change notification system
+.. SPDX-License-Identifier: GPL-2.0
+
+===============================================================
+Inotify - A Powerful yet Simple File Change Notification System
+===============================================================
 
 
 
 Document started 15 Mar 2005 by Robert Love <rml@novell.com>
+
 Document updated 4 Jan 2015 by Zhang Zhen <zhenzhang.zhang@huawei.com>
-	--Deleted obsoleted interface, just refer to manpages for user interface.
+
+	- Deleted obsoleted interface, just refer to manpages for user interface.
 
 (i) Rationale
 
-Q: What is the design decision behind not tying the watch to the open fd of
+Q:
+   What is the design decision behind not tying the watch to the open fd of
    the watched object?
 
-A: Watches are associated with an open inotify device, not an open file.
+A:
+   Watches are associated with an open inotify device, not an open file.
    This solves the primary problem with dnotify: keeping the file open pins
    the file and thus, worse, pins the mount.  Dnotify is therefore infeasible
    for use on a desktop system with removable media as the media cannot be
    unmounted.  Watching a file should not require that it be open.
 
-Q: What is the design decision behind using an-fd-per-instance as opposed to
+Q:
+   What is the design decision behind using an-fd-per-instance as opposed to
    an fd-per-watch?
 
-A: An fd-per-watch quickly consumes more file descriptors than are allowed,
+A:
+   An fd-per-watch quickly consumes more file descriptors than are allowed,
    more fd's than are feasible to manage, and more fd's than are optimally
    select()-able.  Yes, root can bump the per-process fd limit and yes, users
    can use epoll, but requiring both is a silly and extraneous requirement.
@@ -29,8 +38,8 @@ A: An fd-per-watch quickly consumes more file descriptors than are allowed,
    spaces is thus sensible.  The current design is what user-space developers
    want: Users initialize inotify, once, and add n watches, requiring but one
    fd and no twiddling with fd limits.  Initializing an inotify instance two
-   thousand times is silly.  If we can implement user-space's preferences 
-   cleanly--and we can, the idr layer makes stuff like this trivial--then we 
+   thousand times is silly.  If we can implement user-space's preferences
+   cleanly--and we can, the idr layer makes stuff like this trivial--then we
    should.
 
    There are other good arguments.  With a single fd, there is a single
@@ -65,9 +74,11 @@ A: An fd-per-watch quickly consumes more file descriptors than are allowed,
    need not be a one-fd-per-process mapping; it is one-fd-per-queue and a
    process can easily want more than one queue.
 
-Q: Why the system call approach?
+Q:
+   Why the system call approach?
 
-A: The poor user-space interface is the second biggest problem with dnotify.
+A:
+   The poor user-space interface is the second biggest problem with dnotify.
    Signals are a terrible, terrible interface for file notification.  Or for
    anything, for that matter.  The ideal solution, from all perspectives, is a
    file descriptor-based one that allows basic file I/O and poll/select.