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devmap_unload, devmap_load - control validation of memory address translations

#include <sys/ddi.h>
#include <sys/sunddi.h>



int devmap_load(devmap_cookie_t dhp, offset_t off, size_t len,
 uint_t type, uint_t rw);

int devmap_unload(devmap_cookie_t dhp, offset_t off, size_t len);

illumos DDI specific (illumos DDI). dhp off len type rw devmap_unload() and devmap_load() are used to control the validation of the memory mapping described by dhp in the specified range. devmap_unload() invalidates the mapping translations and will generate calls to the devmap_access(9E) entry point next time the mapping is accessed. The drivers use devmap_load() to validate the mapping translations during memory access.

A typical use of devmap_unload() and devmap_load() is in the driver's context management callback function, devmap_contextmgt(9E). To manage a device context, a device driver calls devmap_unload() on the context about to be switched out. It switches contexts, and then calls devmap_load() on the context switched in. devmap_unload() can be used to unload the mappings of other processes as well as the mappings of the calling process, but devmap_load() can only be used to load the mappings of the calling process. Attempting to load another process's mappings with devmap_load() will result in a system panic.

For both routines, the range to be affected is defined by the off and len arguments. Requests affect the entire page containing the off and all pages up to and including the page containing the last byte as indicated by off + len. The arguments type and rw are provided by the system to the calling function (for example, devmap_contextmgt(9E)) and should not be modified.

Supplying a value of 0 for the len argument affects all addresses from the off to the end of the mapping. Supplying a value of 0 for the off argument and a value of 0 for len argument affect all addresses in the mapping.

A non-zero return value from either devmap_unload() or devmap_load() will cause the corresponding operation to fail. The failure may result in a SIGSEGV or SIGBUS signal being delivered to the process.

0 Non-zero These routines can be called from user or kernel context only. Example 1 Managing a One-Page Device Context

The following shows an example of managing a device context that is one page in length.

struct xx_context cur_ctx;

static int
xxdevmap_contextmgt(devmap_cookie_t dhp, void *pvtp, offset_t off,
 size_t len, uint_t type, uint_t rw)
{
 int err;
 devmap_cookie_t cur_dhp;
 struct xx_pvt *p;
 struct xx_pvt *pvp = (struct xx_pvt *)pvtp;
 /* enable access callbacks for the current mapping */
 if (cur_ctx != NULL && cur_ctx != pvp->ctx) {
 p = cur_ctx->pvt;
 /*
 * unload the region from off to the end of the mapping.
 */
 cur_dhp = p->dhp;
 if ((err = devmap_unload(cur_dhp, off, len)) != 0)
 return (err);
 }
 /* Switch device context - device dependent*/
 ...
 /* Make handle the new current mapping */
 cur_ctx = pvp->ctx;
 /*
 * Disable callbacks and complete the access for the
 * mapping that generated this callback.
 */
 return (devmap_load(pvp->dhp, off, len, type, rw));
}

devmap_access (9E), devmap_contextmgt (9E)

Writing Device Drivers