segment – long lived memory segments|
bind '#g' /mnt/segment |
The segment device provides a 2–level file system representing
long–lived sharable segments that processes may segattach(2). The
name of the directory is the class argument to segattach. |
New segments are created under the top level using create (see open(2)). The DMDIR bit must be set in the permissions. Remove(2)'ing the directory makes the segment no longer available for segattach. However, the segment will continue to exist until all processes using it either exit or segdetach it.
Within each segment directory are two files, data and ctl. Reading and writing data affects the contents of the segment. Reading and writing ctl retrieves and sets the segment's properties.
There is only one control message, which sets the segment's virtual
address and length in bytes:
segattach, the address and length arguments are ignored in the call; they are defined only by the va control message. Once the address and length are set, they cannot be reset.
Reading the control file returns a message of the same format with the segment's actual start address and length. For fixed segments, the type and physical base address are appended.
Opening data or reading ctl before setting the virtual address yields the error ``segment not yet allocated''.
The permissions check when segattaching is equivalent to the one
performed when opening data with mode ORDWR.
Create a one megabyte segment at address 0x10000000:|