Hugh Dickins correctly points out that mincore() is actually _supposed_ to fail on an unmapped hole in the user address space, rather than return valid ("empty") information about the hole. This just simplifies the problem further (I had been misled by our previous confusing and complicated way of doing mincore()). Also, in the unlikely situation that we can't allocate a temporary kernel buffer, we should actually return EAGAIN, not ENOMEM, to keep the "unmapped hole" and "allocation failure" error cases separate. Finally, add a comment about our stupid historical lack of support for anonymous mappings. I'll fix that if somebody reminds me after 2.6.20 is out. Acked-by: Hugh Dickins <hugh@veritas.com> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
162 lines
4.2 KiB
C
162 lines
4.2 KiB
C
/*
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* linux/mm/mincore.c
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*
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* Copyright (C) 1994-2006 Linus Torvalds
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*/
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/*
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* The mincore() system call.
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*/
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#include <linux/slab.h>
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#include <linux/pagemap.h>
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#include <linux/mm.h>
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#include <linux/mman.h>
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#include <linux/syscalls.h>
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#include <asm/uaccess.h>
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#include <asm/pgtable.h>
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/*
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* Later we can get more picky about what "in core" means precisely.
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* For now, simply check to see if the page is in the page cache,
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* and is up to date; i.e. that no page-in operation would be required
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* at this time if an application were to map and access this page.
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*/
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static unsigned char mincore_page(struct vm_area_struct * vma,
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unsigned long pgoff)
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{
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unsigned char present = 0;
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struct address_space * as = vma->vm_file->f_mapping;
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struct page * page;
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page = find_get_page(as, pgoff);
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if (page) {
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present = PageUptodate(page);
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page_cache_release(page);
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}
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return present;
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}
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/*
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* Do a chunk of "sys_mincore()". We've already checked
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* all the arguments, we hold the mmap semaphore: we should
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* just return the amount of info we're asked for.
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*/
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static long do_mincore(unsigned long addr, unsigned char *vec, unsigned long pages)
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{
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unsigned long i, nr, pgoff;
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struct vm_area_struct *vma = find_vma(current->mm, addr);
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/*
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* find_vma() didn't find anything above us, or we're
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* in an unmapped hole in the address space: ENOMEM.
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*/
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if (!vma || addr < vma->vm_start)
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return -ENOMEM;
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/*
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* Ok, got it. But check whether it's a segment we support
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* mincore() on. Right now, we don't do any anonymous mappings.
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*
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* FIXME: This is just stupid. And returning ENOMEM is
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* stupid too. We should just look at the page tables. But
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* this is what we've traditionally done, so we'll just
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* continue doing it.
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*/
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if (!vma->vm_file)
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return -ENOMEM;
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/*
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* Calculate how many pages there are left in the vma, and
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* what the pgoff is for our address.
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*/
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nr = (vma->vm_end - addr) >> PAGE_SHIFT;
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if (nr > pages)
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nr = pages;
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pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;
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pgoff += vma->vm_pgoff;
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/* And then we just fill the sucker in.. */
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for (i = 0 ; i < nr; i++, pgoff++)
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vec[i] = mincore_page(vma, pgoff);
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return nr;
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}
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/*
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* The mincore(2) system call.
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*
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* mincore() returns the memory residency status of the pages in the
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* current process's address space specified by [addr, addr + len).
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* The status is returned in a vector of bytes. The least significant
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* bit of each byte is 1 if the referenced page is in memory, otherwise
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* it is zero.
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*
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* Because the status of a page can change after mincore() checks it
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* but before it returns to the application, the returned vector may
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* contain stale information. Only locked pages are guaranteed to
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* remain in memory.
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*
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* return values:
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* zero - success
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* -EFAULT - vec points to an illegal address
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* -EINVAL - addr is not a multiple of PAGE_CACHE_SIZE
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* -ENOMEM - Addresses in the range [addr, addr + len] are
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* invalid for the address space of this process, or
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* specify one or more pages which are not currently
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* mapped
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* -EAGAIN - A kernel resource was temporarily unavailable.
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*/
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asmlinkage long sys_mincore(unsigned long start, size_t len,
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unsigned char __user * vec)
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{
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long retval;
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unsigned long pages;
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unsigned char *tmp;
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/* Check the start address: needs to be page-aligned.. */
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if (start & ~PAGE_CACHE_MASK)
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return -EINVAL;
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/* ..and we need to be passed a valid user-space range */
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if (!access_ok(VERIFY_READ, (void __user *) start, len))
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return -ENOMEM;
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/* This also avoids any overflows on PAGE_CACHE_ALIGN */
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pages = len >> PAGE_SHIFT;
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pages += (len & ~PAGE_MASK) != 0;
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if (!access_ok(VERIFY_WRITE, vec, pages))
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return -EFAULT;
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tmp = (void *) __get_free_page(GFP_USER);
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if (!tmp)
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return -EAGAIN;
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retval = 0;
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while (pages) {
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/*
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* Do at most PAGE_SIZE entries per iteration, due to
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* the temporary buffer size.
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*/
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down_read(¤t->mm->mmap_sem);
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retval = do_mincore(start, tmp, max(pages, PAGE_SIZE));
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up_read(¤t->mm->mmap_sem);
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if (retval <= 0)
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break;
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if (copy_to_user(vec, tmp, retval)) {
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retval = -EFAULT;
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break;
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}
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pages -= retval;
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vec += retval;
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start += retval << PAGE_SHIFT;
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retval = 0;
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}
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free_page((unsigned long) tmp);
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return retval;
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}
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