118 lines
2.3 KiB
Text
118 lines
2.3 KiB
Text
|
.TH SEGMENT 3
|
||
|
|
.SH NAME
|
||
|
|
segment \- long lived memory segments
|
||
|
|
.SH SYNOPSIS
|
||
|
|
.nf
|
||
|
|
.B bind '#g' /mnt/segment
|
||
|
|
|
||
|
|
.BI #g/ seg1
|
||
|
|
.BI #g/ seg1 /ctl
|
||
|
|
.BI #g/ seg1 /data
|
||
|
|
.BI #g/ seg2
|
||
|
|
.BI #g/ seg2 /ctl
|
||
|
|
.BI #g/ seg2 /data
|
||
|
|
...
|
||
|
|
.fi
|
||
|
|
.SH DESCRIPTION
|
||
|
|
.PP
|
||
|
|
The
|
||
|
|
.I segment
|
||
|
|
device provides a 2-level file system representing
|
||
|
|
long-lived sharable segments that processes may
|
||
|
|
.IR segattach (2).
|
||
|
|
The name of the directory is the
|
||
|
|
.I class
|
||
|
|
argument to
|
||
|
|
.IR segattach .
|
||
|
|
.PP
|
||
|
|
New segments are created under the top level
|
||
|
|
using
|
||
|
|
.B create
|
||
|
|
(see
|
||
|
|
.IR open (2)).
|
||
|
|
The
|
||
|
|
.B DMDIR
|
||
|
|
bit must be set in the permissions.
|
||
|
|
.IR Remove (2)'ing
|
||
|
|
the directory makes the segment no longer
|
||
|
|
available for
|
||
|
|
.IR segattach .
|
||
|
|
However, the segment will continue to exist until all
|
||
|
|
processes using it either exit or
|
||
|
|
.I segdetach
|
||
|
|
it.
|
||
|
|
.PP
|
||
|
|
Within each segment directory are two files,
|
||
|
|
.B data
|
||
|
|
and
|
||
|
|
.BR ctl .
|
||
|
|
Reading and writing
|
||
|
|
.B data
|
||
|
|
affects the contents of the segment.
|
||
|
|
Reading and writing
|
||
|
|
.B ctl
|
||
|
|
retrieves and sets the segment's properties.
|
||
|
|
.PP
|
||
|
|
There is only one control message, which sets the segment's
|
||
|
|
virtual address and length in bytes:
|
||
|
|
.EX
|
||
|
|
va \fIaddress length\fP
|
||
|
|
.EE
|
||
|
|
.I Address
|
||
|
|
is automatically rounded down to a page boundary and
|
||
|
|
.I length
|
||
|
|
is rounded up to end the segment at a page boundary.
|
||
|
|
The segment will reside at the same virtual address in
|
||
|
|
all processes sharing it.
|
||
|
|
When the segment
|
||
|
|
is attached using
|
||
|
|
.IR segattach,
|
||
|
|
the address and length arguments are ignored in the call;
|
||
|
|
they are defined only by the
|
||
|
|
.B va
|
||
|
|
control message.
|
||
|
|
Once the address and length are set, they cannot be reset.
|
||
|
|
.PP
|
||
|
|
Reading the control file
|
||
|
|
returns a message of the same format with the segment's actual
|
||
|
|
start address and length.
|
||
|
|
.PP
|
||
|
|
Opening
|
||
|
|
.B data
|
||
|
|
or reading
|
||
|
|
.B ctl
|
||
|
|
before setting the virtual address yields the error
|
||
|
|
``segment not yet allocated''.
|
||
|
|
.PP
|
||
|
|
The permissions check when
|
||
|
|
.IR segattach ing
|
||
|
|
is equivalent to the one performed when opening
|
||
|
|
.B data
|
||
|
|
with mode ORDWR.
|
||
|
|
.SH EXAMPLE
|
||
|
|
.PP
|
||
|
|
Create a one megabyte segment at address 0x10000000:
|
||
|
|
.EX
|
||
|
|
% bind '#g' /mnt/segment
|
||
|
|
% mkdir /mnt/segment/example
|
||
|
|
% echo 'va 0x10000000 0x100000' > /mnt/segment/example/ctl
|
||
|
|
.EE
|
||
|
|
.PP
|
||
|
|
Put the string ``hi mom'' at the start of the segment:
|
||
|
|
.EX
|
||
|
|
% echo -n hi mom > /mnt/segment/example/data
|
||
|
|
.EE
|
||
|
|
.PP
|
||
|
|
Attach the segment to a process:
|
||
|
|
.EX
|
||
|
|
{
|
||
|
|
ulong va;
|
||
|
|
|
||
|
|
va = segattach(0, "example", 0, 0);
|
||
|
|
}
|
||
|
|
.EE
|
||
|
|
.SH "SEE ALSO
|
||
|
|
.IR segattach (2)
|
||
|
|
.SH SOURCE
|
||
|
|
.B /sys/src/9/port/devsegment.c
|