z/VM: CP Commands and Utilities Reference - z/VM - IBM

DEFSEG
If other pages in the segment have been defined with the exclusive attribute
(page descriptor codes ER, EW, and EN), any pages not specified on the
command line become exclusive read/write pages whose data are not saved.
This corresponds to page descriptor code EN.
The page ranges of a member saved segment cannot overlap with the specified
page ranges of another member saved segment associated with the same
segment space. Areas not specified (defaulted to “no data saved”) may be
taken by another member saved segment. If the member uses these pages but
doesn’t need the data from the pages saved, the range with the EN or SN
attribute type must be specified. Also, this member saved segment’s range
descriptor code cannot conflict with those of an existing member that has
ranges defined in the same segment of storage.
The page number is a hexadecimal value less than or equal to X'7FEFF' (2047
MB). The following list shows examples of how hexadecimal storage addresses
translate into hexadecimal page numbers:
Storage Address
Page Number
00000xxx
0
00001xxx
1
00022xxx
22
00333xxx
333
04444xxx
4444
7F800xxx
7F800
type
refers to the page descriptor code of the page range in the saved segment. It
indicates the type of virtual machine access permitted to pages in the range.
The first character is either E for exclusive access or S for shared access.
Sharing of storage between virtual machines is based on 1 MB segments, so all
256 pages in any one segment must be either exclusive or shared.
The second character of the page descriptor code defines the storage
protection characteristics of the page. These character designators follow:
v R indicates that page protection is used to make the page range read-only.
v W means that the page is not protected, and users have read/write access.
v N stands for “read/write, no data saved,” meaning that the page is treated as
a new page when the user refers to it. The contents of, and storage keys for,
“no data saved” pages are not saved by the SAVESEG command.
v C stands for “CP-writable, virtual machine read-only, no data saved,”
meaning virtual machines have read-only access to these pages, but CP
services may change the data in the pages.
(The SC page descriptor code cannot be used with the LOADNSHR
operand.)
The contents of storage keys for “no data saved” pages are not saved by the
SAVESEG command.
Valid page descriptor codes are:
206 z/VM: CP Commands and Utilities Reference