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, if the file
name is unacceptable, if the user does not have permission
to open it as requested (see sys-stat(2) for a description
of permissions), or if any other error occurs.
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. The bits in perm are
the same as those in the file mode returned by sys-stat(2).
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->DMDIR bit
is set in perm, and omode is Sys->OREAD. The file will be
exclusive-use if the Sys->DMEXCL bit is set in perm and the
underlying file server supports it; see open(5) for details.
It will be append-only if the Sys->DMAPPEND bit is set, and
the underlying file server supports it.
Create returns nil if the path up to the last element of
file cannot be evaluated, if the file name is unacceptable,
if the user does not have write permission in the final
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SYS-OPEN(2) SYS-OPEN(2)
directory, if the file already exists and does not permit
the access defined by omode, or if any other error occurs.
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).
Since create may succeed even if the file exists, a special
mechanism is necessary for applications that require an
atomic create operation. If the Sys->OEXCL bit is set in
the mode for a create, the call succeeds only if the file
does not already exist; see open(5) for details.
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)
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