ref: 9adaf2e7f8a81eb207eb7894e80864019950e0e7
dir: /sys/man/3/segment/
.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 type\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. Optionally, .I type can be specified as .B fixed to create a physically continuous segment with a fixed physical base address suitable for hardware DMA access. 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. For .B fixed segments, the type and physical base address are appended. .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