ref: 5edeca01b0622463a65c126ebcc29314013fd928
dir: /man/3/fs/
.TH FS 3 emu
.SH NAME
fs \- host file system interface
.SH SYNOPSIS
.EX
bind #U\fIspec\fP /
sys->bind("#U\fIspec\fP", "/", Sys->MAFTER|Sys->MCREATE);
.EE
.SH DESCRIPTION
.I Fs
provides an interface to the host file system when running
.IR emu (1).
The device is automatically bound to the root of the Inferno namespace when
.I emu
starts.
.I Fs
maps filenames from the Inferno namespace to the real host filesystem
namespace. The mapping is determined by the host system directory that
.I emu
serves (see the description of the
.B -r
option in
.IR emu (1)).
.PP
The plain name
.B #U
always refers to the root of the Inferno tree within the host file system.
An optional
.I spec
string can select a different tree using conventions peculiar to the host system type.
Currently, on Unix and Plan 9, a
.I spec
of
.B *
(ie,
.BR #U* )
refers to the root of the host system;
on Windows, the
.I spec
can give a device letter (eg,
.BR #Uc: )
to refer to the Windows tree on that device.
.PP
When there is nothing but
.IR root (3)
in the name space, the device can only be bound from Limbo using
.IR sys-bind (2)
as shown above, since there is nothing in the name space
to support either
.IR bind (1)
or
.IR newns (2).
It can later be rebound elsewhere in the name space using
.IR bind (1).
.PP
.I Fs
provides only an approximation to the
file ownership and permissions checking defined in
.IR intro (5)
and other entries in this manual.
.IR Emu (1)
typically runs as the user that starts it, and that user will own all newly-created
files and directories, and that user's host system access rights control access
to any file.
Other details are specific to the host system, as given below.
.PP
The set of characters visible in file names within
.I fs
is also determined by the host operating system, not Inferno.
For instance, names might contain control characters, or even `/',
which might render them unusable in Inferno.
.SS Unix
When checking owner, group and other permissions, the intent in Inferno is that
each is tried in turn, in that order.
Unix checks just the first that applies, so that if group
permission disallows access but other allows it, the access is still denied.
If
.IR emu (1)
is run as the super-user, Inferno's rules for ownership and permission checking are enforced by
.I fs
itself; otherwise, Unix's permission checking prevails.
.PP
On MacOS X, file names might be case insensitive, depending on file system settings.
.SS FAT file system (Windows9x and Windows/NT)
The values of
.B uid
and
.B gid
are
.BR Everyone .
.PP
Files and directories always have read and execute permission,
which cannot be changed.
Files without write permission cannot be removed.
.SS NTFS file system (Windows/NT, 2000, XP)
Permissions for read, write and execute operates as described in
.IR sys-stat (2).
.IR Emu (1)
attempts to maintain a limited
but consistent map between Inferno and NT worlds, specifically between Inferno names
and NT security IDs.
Special NT group
.B Everyone
represents `other' for file permissions.
The Inferno
.B uid
is the file owner under NT;
the Inferno
.B gid
reported is the first user in the file's ACL
that is neither the owner nor
.BR Everyone ;
failing that, the
.B gid
is the file's owner.
.SH SOURCE
.B /emu/*/devfs.c
.br
.B /emu/port/devfs-posix.c