89 lines
1.8 KiB
C
89 lines
1.8 KiB
C
// Physical memory allocator, intended to allocate
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// memory for user processes, kernel stacks, page table pages,
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// and pipe buffers. Allocates 4096-byte pages.
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#include "types.h"
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#include "defs.h"
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#include "param.h"
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#include "memlayout.h"
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#include "mmu.h"
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#include "spinlock.h"
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struct run {
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struct run *next;
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};
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struct {
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struct spinlock lock;
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struct run *freelist;
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} kmem;
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extern char end[]; // first address after kernel loaded from ELF file
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static char *newend;
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// A simple page allocator to get off the ground during entry
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char *
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enter_alloc(void)
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{
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if (newend == 0)
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newend = end;
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if ((uint) newend >= KERNBASE + 0x400000)
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panic("only first 4Mbyte are mapped during entry");
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void *p = (void*)PGROUNDUP((uint)newend);
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memset(p, 0, PGSIZE);
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newend = newend + PGSIZE;
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return p;
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}
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// Initialize free list of physical pages.
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void
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kinit(void)
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{
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char *p;
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initlock(&kmem.lock, "kmem");
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p = (char*)PGROUNDUP((uint)newend);
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for(; p + PGSIZE <= (char*)p2v(PHYSTOP); p += PGSIZE)
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kfree(p);
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}
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//PAGEBREAK: 21
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// Free the page of physical memory pointed at by v,
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// which normally should have been returned by a
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// call to kalloc(). (The exception is when
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// initializing the allocator; see kinit above.)
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void
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kfree(char *v)
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{
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struct run *r;
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if((uint)v % PGSIZE || v < end || v2p(v) >= PHYSTOP)
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panic("kfree");
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// Fill with junk to catch dangling refs.
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memset(v, 1, PGSIZE);
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acquire(&kmem.lock);
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r = (struct run*)v;
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r->next = kmem.freelist;
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kmem.freelist = r;
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release(&kmem.lock);
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}
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// Allocate one 4096-byte page of physical memory.
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// Returns a pointer that the kernel can use.
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// Returns 0 if the memory cannot be allocated.
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char*
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kalloc(void)
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{
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struct run *r;
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acquire(&kmem.lock);
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r = kmem.freelist;
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if(r)
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kmem.freelist = r->next;
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release(&kmem.lock);
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return (char*)r;
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}
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