Creates pretranslation data structures.
int xlate_create (dp, baddr, count, flags)
struct xmem*dp;
caddr_t baddr;
int count;
uint flags;The xlate_create kernel service creates pretranslation data structures capable of pretranslating all pages of the virtual buffer indicated by the baddr parameter for length of count into a list of physical page numbers, appended to the cross memory descriptor pointed to by dp.
If the XLATE_ALLOC flag is set, only the data structures are created and no pretranslation is done. If the flag is not set, in addition to the data structures being created, each page of the buffer is translated and the access permissions verified, requiring read-write access to each page. The XLATE_ALLOC flag is useful when the buffer will be pinned and utilized later, through the xlate_pin and xlate_unpin kernel services.
The XLATE_SPARSE flag can be used to indicate that only selected portions of a pretranslated region may be valid (pinned and pretranslated) at any given time. The XLATE_SPARSE flag can be used in conjunction with the XLATE_ALLOC flag to preallocate the pretranslation data structures for an address region that will be dynamically managed.
The xlate_create kernel service is primarily for use when memory buffers will be reused for I/O. The use of this service to create a pretranslation for the memory buffer avoids page translation and access checking overhead for all future DMAs involving the memory buffer until the xlate_remove kernel service is called.
| Item | Description |
|---|---|
| dp | Points to the cross memory descriptor. |
| baddr | Points to the virtual buffer. |
| count | Specifies the length of the virtual buffer. |
| flags | Specifies the operation. Valid values are as
follows:
|
| Item | Description |
|---|---|
| ENOMEM | Unable to allocate memory |
| XMEM_FAIL | No physical translation, or No Access to a Page |
| XMEM_SUCC | Successful pretranslation created |
The xlate_create kernel service can only be called from the process environment. The entire buffer must be pinned (unless the XLATE_ALLOC flag is set), and the cross memory descriptor valid.