91 lines
2.3 KiB
C
91 lines
2.3 KiB
C
// implement fork from user space
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#include <inc/string.h>
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#include <inc/lib.h>
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// PTE_COW marks copy-on-write page table entries.
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// It is one of the bits explicitly allocated to user processes (PTE_AVAIL).
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#define PTE_COW 0x800
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//
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// Custom page fault handler - if faulting page is copy-on-write,
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// map in our own private writable copy.
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//
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static void
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pgfault(struct UTrapframe *utf)
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{
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void *addr = (void *) utf->utf_fault_va;
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uint32_t err = utf->utf_err;
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int r;
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// Check that the faulting access was (1) a write, and (2) to a
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// copy-on-write page. If not, panic.
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// Hint:
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// Use the read-only page table mappings at uvpt
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// (see <inc/memlayout.h>).
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// LAB 4: Your code here.
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// Allocate a new page, map it at a temporary location (PFTEMP),
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// copy the data from the old page to the new page, then move the new
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// page to the old page's address.
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// Hint:
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// You should make three system calls.
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// LAB 4: Your code here.
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panic("pgfault not implemented");
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}
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//
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// Map our virtual page pn (address pn*PGSIZE) into the target envid
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// at the same virtual address. If the page is writable or copy-on-write,
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// the new mapping must be created copy-on-write, and then our mapping must be
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// marked copy-on-write as well. (Exercise: Why do we need to mark ours
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// copy-on-write again if it was already copy-on-write at the beginning of
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// this function?)
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//
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// Returns: 0 on success, < 0 on error.
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// It is also OK to panic on error.
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//
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static int
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duppage(envid_t envid, unsigned pn)
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{
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int r;
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// LAB 4: Your code here.
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panic("duppage not implemented");
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return 0;
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}
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//
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// User-level fork with copy-on-write.
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// Set up our page fault handler appropriately.
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// Create a child.
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// Copy our address space and page fault handler setup to the child.
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// Then mark the child as runnable and return.
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//
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// Returns: child's envid to the parent, 0 to the child, < 0 on error.
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// It is also OK to panic on error.
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//
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// Hint:
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// Use uvpd, uvpt, and duppage.
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// Remember to fix "thisenv" in the child process.
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// Neither user exception stack should ever be marked copy-on-write,
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// so you must allocate a new page for the child's user exception stack.
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//
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envid_t
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fork(void)
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{
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// LAB 4: Your code here.
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panic("fork not implemented");
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}
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// Challenge!
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int
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sfork(void)
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{
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panic("sfork not implemented");
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return -E_INVAL;
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}
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