SYS-OPEN(2) SYS-OPEN(2)
NAME
open, create - open a file for reading or writing, create
file
SYNOPSIS
include "sys.m";
sys := load Sys Sys->PATH;
create: fn(file: string, omode, perm: int): ref FD;
open: fn(file: string, omode: int): ref FD;
DESCRIPTION
Open opens the file for I/O and returns an associated file
descriptor. Omode is one of Sys->OREAD, Sys->OWRITE, or
Sys->ORDWR, asking for permission to read, write, or read
and write, respectively. There are two values that can be
OR'd with those to form omode: Sys->OTRUNC says to truncate
the file before opening it, which requires write permission
even if omode is Sys->OREAD; and Sys->ORCLOSE says to remove
the file when it is closed (ie, when the last reference to
this file descriptor goes away).
Open returns nil if the file does not exist or the user does
not have permission to open it as requested (see sys-stat(2)
for a description of permissions).
Create creates a new file or prepares to rewrite an existing
file, opens it according to omode (as described for open),
and returns an associated file descriptor.
If the file is new, the owner is set to the user id of the
creating process group, the group to that of the containing
directory, and the permissions to perm ANDed with the per-
missions of the containing directory.
If the file already exists, it is truncated to 0 length, but
the permissions, owner, and group remain unchanged.
The created file will be a directory if the Sys->CHDIR bit
is set in perm, and omode is Sys->OREAD.
Create returns nil if the path up to the last element of
file cannot be evaluated, if the user does not have write
permission in the final directory, or if the file already
exists and does not permit the access defined by omode.
If the file is new and the directory in which it is created
is a union directory (see sys-intro(2)) then the constituent
directory where the file is created depends on the structure
of the union: see sys-bind(2).
Page 1 Plan 9 (printed 11/18/24)
SYS-OPEN(2) SYS-OPEN(2)
There is no explicit ``close'' routine: when the last refer-
ence to the file descriptor is released, the system closes
the associated file. For devices and network protocols
where shutdown must be guaranteed, write a hangup message to
the associated control file and use the return value of the
write to verify closure.
SEE ALSO
sys-intro(2), sys-bind(2), sys-stat(2)
Page 2 Plan 9 (printed 11/18/24)