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/* libbdev - driver endpoint management */
#include <minix/drivers.h>
#include <minix/bdev.h>
#include <minix/ds.h>
#include <assert.h>
#include "const.h"
#include "type.h"
#include "proto.h"
static struct {
endpoint_t endpt;
char label[DS_MAX_KEYLEN];
} driver_tab[NR_DEVICES];
void bdev_driver_init(void)
{
/* Initialize the driver table.
*/
int i;
for (i = 0; i < NR_DEVICES; i++) {
driver_tab[i].endpt = NONE;
driver_tab[i].label[0] = '\0';
}
}
void bdev_driver_clear(dev_t dev)
{
/* Clear information about a driver.
*/
int major;
major = major(dev);
assert(major >= 0 && major < NR_DEVICES);
driver_tab[major].endpt = NONE;
driver_tab[major].label[0] = '\0';
}
endpoint_t bdev_driver_set(dev_t dev, char *label)
{
/* Set the label for a driver, and retrieve the associated endpoint.
*/
int major;
major = major(dev);
assert(major >= 0 && major < NR_DEVICES);
assert(strlen(label) < sizeof(driver_tab[major].label));
strlcpy(driver_tab[major].label, label, sizeof(driver_tab[major].label));
driver_tab[major].endpt = NONE;
return bdev_driver_update(dev);
}
endpoint_t bdev_driver_get(dev_t dev)
{
/* Return the endpoint for a driver, or NONE if we do not know its endpoint.
*/
int major;
major = major(dev);
assert(major >= 0 && major < NR_DEVICES);
return driver_tab[major].endpt;
}
endpoint_t bdev_driver_update(dev_t dev)
{
/* Update the endpoint of a driver. The caller of this function already knows
* that the current endpoint may no longer be valid, and must be updated.
* Return the new endpoint upon success, and NONE otherwise.
*/
endpoint_t endpt;
int r, major, nr_tries;
major = major(dev);
assert(major >= 0 && major < NR_DEVICES);
assert(driver_tab[major].label[0] != '\0');
/* Repeatedly retrieve the endpoint for the driver label, and see if it is a
* different, valid endpoint. If retrieval fails at first, we have to wait.
* We use polling, as opposed to a DS subscription, for a number of reasons:
* 1) DS supports only one subscription per process, and our main program may
* already have a subscription;
* 2) if we block on receiving a notification from DS, we cannot impose an
* upper bound on the retry time;
* 3) temporarily subscribing and then unsubscribing may cause leftover DS
* notifications, which the main program would then have to deal with.
* As of writing, unsubscribing from DS is not possible at all, anyway.
*
* In the normal case, the driver's label/endpoint mapping entry disappears
* completely for a short moment, before being replaced with the new mapping.
* Hence, failure to retrieve the entry at all does not constitute permanent
* failure. In fact, there is no way to determine reliably that a driver has
* failed permanently in the current approach. For this we simply rely on the
* retry limit.
*/
for (nr_tries = 0; nr_tries < DS_NR_TRIES; nr_tries++) {
r = ds_retrieve_label_endpt(driver_tab[major].label, &endpt);
if (r == OK && endpt != NONE && endpt != driver_tab[major].endpt) {
driver_tab[major].endpt = endpt;
return endpt;
}
if (nr_tries < DS_NR_TRIES - 1)
micro_delay(DS_DELAY);
}
driver_tab[major].endpt = NONE;
return NONE;
}
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