filesystems.5, erofs.5: add erofs documentation

Modelled after tmpfs(5) ‒ there's a listing of mount options, and a
summary of limitations.  The feature flags are described in mkfs.erofs,
and they're versioned and maintained upstream quite well there, so no
need to duplicate those, since you only care on image creation.

The real value add is the mount options, but I cannot figure out how
device_id and fsid interact with the system at large, so I just noted
they're there.

State as of Linux 6.3-rc5.

Also, remove explicit .TP indent in filesystems.5 since we're already
touching this hunk: all entries sans iso9660 and Reiserfs fall within
the default prevailing indent, so no need to specify a wide one.

Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Signed-off-by: Alejandro Colomar <alx@kernel.org>

2 files changed, 102 insertions, 1 deletions

diff --git a/man5/erofs.5 b/man5/erofs.5
new file mode 100644
index 000000000..933e830b8
--- /dev/null
+++ b/man5/erofs.5
@@ -0,0 +1,95 @@
+.\" Copyright (c) 2016 by Michael Kerrisk <mtk.manpages@gmail.com>
+.\"
+.\" SPDX-License-Identifier: Linux-man-pages-copyleft
+.\"
+.TH erofs 5 (date) "Linux man-pages (unreleased)"
+.SH NAME
+erofs \- the Enhanced Read-Only File System
+.SH DESCRIPTION
+.B erofs
+is a create-once read-only filesystem,
+with support for compression and a multi-device backing store.
+.PP
+There are two inode formats:
+.br
+\[bu] 32-byte compact with 16-bit UID/GID, 32-bit file size, and no file times,
+and
+.br
+\[bu] 64-byte extended with 32-bit UID/GID, 64-bit file size,
+and a modification time
+.RI ( st_mtim ).
+.\" See fs/erofs/super.c:shmem_parse_options for options it supports.
+.SS Mount options
+.TP
+.B user_xattr
+.TQ
+.B nouser_xattr
+Controls whether
+.I user
+extended attributes are exposed.
+Defaults to yes.
+.TP
+.B acl
+.TQ
+.B noacl
+Controls whether POSIX
+.BR acl (5)s
+are exposed.
+Defaults to yes.
+.TP
+.BR cache_strategy = disabled | readahead | readaround
+Cache allocation for compressed files:
+never, if reading from start of file, regardless of position.
+Defaults to
+.BR readaround .
+.TP
+.BR dax
+.TQ
+.BR dax = always | never
+Direct Access control.
+If
+.B always
+and the source device supports DAX, uncompressed non-inlined files
+will be read directly, without going through the page cache.
+.B dax
+is a synonym for
+.BR always .
+Defaults to unset, which is equivalent to
+.BR never .
+.TP
+.BR device = \fIblobdev\fP
+Add extra device holding some of the data.
+Must be given as many times and in the same order as
+.B \-\-blobdev
+was to
+.BR mkfs.erofs (1).
+.\" Nominally there's a device_table feature and it somehow scans(?) for them,
+.\" cf. super.c:erofs_scan_devices(), but I haven't gotten it to work
+.TP
+.BR domain_id = \fIdid\fP
+.TQ
+.BR fsid = \fIid\fP
+Control CacheFiles on-demand read support.
+To be documented.
+.RE
+.IP
+.SH VERSIONS
+.B erofs
+images are versioned through the use of feature flags;
+these are listed in the
+.B \-E
+section of
+.BR mkfs.erofs (1),
+.SH CONFIGURATION
+Linux must be configured with the
+.B CONFIG_EROFS_FS
+option to mount EROFS filesystems.
+There are sub-configuration items that restrict the availability
+of some of the parameters above.
+.SH SEE ALSO
+.BR mkfs.erofs (1),
+.BR fsck.erofs (1),
+.BR dump.erofs (1)
+.PP
+.I Documentation/filesystems/erofs.txt
+in the Linux source.
diff --git a/man5/filesystems.5 b/man5/filesystems.5
index 3c15f14da..ba795f956 100644
--- a/man5/filesystems.5
+++ b/man5/filesystems.5
@@ -47,7 +47,13 @@ short description of the available or historically available
 filesystems in the Linux kernel.
 See the kernel documentation for a comprehensive
 description of all options and limitations.
-.TP 10
+.TP
+.B erofs
+is the Enhanced Read-Only File System, stable since Linux 5.4.
+.\" commit 47e4937a4a7ca4184fd282791dfee76c6799966a moves it out of staging
+See
+.BR erofs (5).
+.TP
 .B ext
 is an elaborate extension of the
 .B minix