FS(3) (emu) FS(3)
NAME
fs - host file system interface
SYNOPSIS
bind #Uspec /
sys->bind("#Uspec", "/", Sys->MAFTER|Sys->MCREATE);
DESCRIPTION
Fs provides an interface to the host file system when run-
ning emu(1). The device is automatically bound to the root
of the Inferno namespace when emu starts. Fs maps filenames
from the Inferno namespace to the real host filesystem
namespace. The mapping is determined by the host system
directory that emu serves (see the description of the -r
option in emu(1)).
The plain name #U always refers to the root of the Inferno
tree within the host file system. An optional spec string
can select a different tree using conventions peculiar to
the host system type. Currently, on Unix and Plan 9, a spec
of * (ie, #U*) refers to the root of the host system; on
Windows, the spec can give a device letter (eg, #Uc:) to
refer to the Windows tree on that device.
When there is nothing but root(3) in the name space, the
device can only be bound from Limbo using sys-bind(2) as
shown above, since there is nothing in the name space to
support either bind(1) or newns(2). It can later be rebound
elsewhere in the name space using bind(1).
Fs provides only an approximation to the file ownership and
permissions checking defined in intro(5) and other entries
in this manual. 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.
The set of characters visible in file names within 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.
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 emu(1) is run as the super-user,
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FS(3) (emu) FS(3)
Inferno's rules for ownership and permission checking are
enforced by fs itself; otherwise, Unix's permission checking
prevails.
On MacOS X, file names might be case insensitive, depending
on file system settings.
FAT file system (Windows9x and Windows/NT)
The values of uid and gid are Everyone.
Files and directories always have read and execute permis-
sion, which cannot be changed. Files without write permis-
sion cannot be removed.
NTFS file system (Windows/NT, 2000, XP)
Permissions for read, write and execute operates as
described in sys-stat(2). Emu(1) attempts to maintain a lim-
ited but consistent map between Inferno and NT worlds,
specifically between Inferno names and NT security IDs.
Special NT group Everyone represents `other' for file per-
missions. The Inferno uid is the file owner under NT; the
Inferno gid reported is the first user in the file's ACL
that is neither the owner nor Everyone; failing that, the
gid is the file's owner.
SOURCE
/emu/*/devfs.c
/emu/port/devfs-posix.c
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