minix/kernel/system/do_segctl.c

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/* The system call implemented in this file:
* m_type: SYS_SEGCTL
*
* The parameters for this system call are:
* m4_l3: SEG_PHYS (physical base address)
* m4_l4: SEG_SIZE (size of segment)
* m4_l1: SEG_SELECT (return segment selector here)
* m4_l2: SEG_OFFSET (return offset within segment here)
* m4_l5: SEG_INDEX (return index into remote memory map here)
*/
#include "../system.h"
#include "../protect.h"
#if USE_SEGCTL
/*===========================================================================*
* do_segctl *
*===========================================================================*/
PUBLIC int do_segctl(m_ptr)
register message *m_ptr; /* pointer to request message */
{
/* Return a segment selector and offset that can be used to reach a physical
* address, for use by a driver doing memory I/O in the A0000 - DFFFF range.
*/
u16_t selector;
vir_bytes offset;
int i, index;
register struct proc *rp;
phys_bytes phys = (phys_bytes) m_ptr->SEG_PHYS;
vir_bytes size = (vir_bytes) m_ptr->SEG_SIZE;
int result;
/* First check if there is a slot available for this segment. */
rp = proc_addr(m_ptr->m_source);
index = -1;
for (i=0; i < NR_REMOTE_SEGS; i++) {
if (! rp->p_priv->s_farmem[i].in_use) {
index = i;
rp->p_priv->s_farmem[i].in_use = TRUE;
rp->p_priv->s_farmem[i].mem_phys = phys;
rp->p_priv->s_farmem[i].mem_len = size;
break;
}
}
if (index < 0) return(ENOSPC);
if (! machine.protected) {
selector = phys / HCLICK_SIZE;
offset = phys % HCLICK_SIZE;
result = OK;
} else {
/* Check if the segment size can be recorded in bytes, that is, check
* if descriptor's limit field can delimited the allowed memory region
* precisely. This works up to 1MB. If the size is larger, 4K pages
* instead of bytes are used.
*/
if (size < BYTE_GRAN_MAX) {
init_dataseg(&rp->p_ldt[EXTRA_LDT_INDEX+i], phys, size,
USER_PRIVILEGE);
selector = ((EXTRA_LDT_INDEX+i)*0x08) | (1*0x04) | USER_PRIVILEGE;
offset = 0;
result = OK;
} else {
init_dataseg(&rp->p_ldt[EXTRA_LDT_INDEX+i], phys & ~0xFFFF, 0,
USER_PRIVILEGE);
selector = ((EXTRA_LDT_INDEX+i)*0x08) | (1*0x04) | USER_PRIVILEGE;
offset = phys & 0xFFFF;
result = OK;
}
}
/* Request successfully done. Now return the result. */
m_ptr->SEG_INDEX = index | REMOTE_SEG;
m_ptr->SEG_SELECT = selector;
m_ptr->SEG_OFFSET = offset;
return(result);
}
#endif /* USE_SEGCTL */