sysfs.5: New page documenting the sysfs filesystem

Just a skeleton page so far, but perhaps it will be filled out
over time.

Reported-by: Mark Wielaard <mark@klomp.org>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man5/sysfs.5

@@ -0,0 +1,114 @@
+.\" Copyright (c) 2017 by Michael Kerrisk <mtk.manpages@gmail.com>
+.\"
+.\" %%%LICENSE_START(VERBATIM)
+.\" Permission is granted to make and distribute verbatim copies of this
+.\" manual provided the copyright notice and this permission notice are
+.\" preserved on all copies.
+.\"
+.\" Permission is granted to copy and distribute modified versions of this
+.\" manual under the conditions for verbatim copying, provided that the
+.\" entire resulting derived work is distributed under the terms of a
+.\" permission notice identical to this one.
+.\"
+.\" Since the Linux kernel and libraries are constantly changing, this
+.\" manual page may be incorrect or out-of-date.  The author(s) assume no
+.\" responsibility for errors or omissions, or for damages resulting from
+.\" the use of the information contained herein.  The author(s) may not
+.\" have taken the same level of care in the production of this manual,
+.\" which is licensed free of charge, as they might when working
+.\" professionally.
+.\"
+.\" Formatted or processed versions of this manual, if unaccompanied by
+.\" the source, must acknowledge the copyright and authors of this work.
+.\" %%%LICENSE_END
+.\"
+.TH SYSFS 5 2017-09-10 "Linux" "Linux Programmer's Manual"
+.SH NAME
+sysfs \- a filesystem for exporting kernel objects
+.SH DESCRIPTION
+The
+.B sysfs
+filesystem is a pseudo-filesystem which provides an interface to
+kernel data structures.
+(More precisely, the files and directories in
+.B sysfs
+provide a view of the
+.IR kobject
+structures defined internally within the kernel.)
+The files under
+.B sysfs
+provide information about devices, kernel modules, filesystems,
+and other kernel components.
+.PP
+The
+.B sysfs
+filesystem is commonly mounted at
+.IR /sys .
+Typically, it is mounted automatically by the system,
+but it can also be mounted manually using a command such as:
+.PP
+.in +4n
+.EX
+mount \-t sysfs sysfs /sys
+.EE
+.in
+.PP
+Many of the files in the
+.B sysfs
+filesystem are read-only,
+but some files are writable, allowing kernel variables to be changed.
+.\"
+.SS Files and directories
+The following list describes some of the files and directories under the
+.I /sys
+hierarchy.
+.TP
+.IR /sys/block
+.TP
+.IR /sys/bus
+.TP
+.IR /sys/class
+.TP
+.IR /sys/dev
+.TP
+.IR /sys/devices
+.TP
+.IR /sys/firmware
+.TP
+.IR /sys/fs
+.TP
+.IR /sys/fs/cgroup
+This directory conventionally is used as a mount point for a
+.BR tmpfs (5)
+filesystem containing mount points for
+.BR cgroups (7)
+filesystems.
+.TP
+.IR /sys/hypervisor
+.TP
+.IR /sys/kernel
+.TP
+.IR /sys/module
+.TP
+.IR /sys/power
+.SH VERSIONS
+The
+.B sysfs
+filesystem first appeared in Linux 2.6.0.
+.SH CONFORMING TO
+The
+.B sysfs
+filesystem is Linux-specific.
+.SH NOTES
+This manual page is incomplete, possibly inaccurate, and is the kind
+of thing that needs to be updated very often.
+.SH SEE ALSO
+.BR proc (5),
+.BR udev (7)
+.PP
+The kernel source file
+.I Documentation/filesystems/sysfs.txt
+and various other files in
+.IR Documentation/ABI
+and
+.IR Documentation/*/sysfs.txt