On Sun, Jul 14, 2013 at 7:17 AM, Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
> On 07/11, Colin Cross wrote:
>>
>> +static void seq_print_vma_name(struct seq_file *m, struct vm_area_struct *vma)
>> +{
>> + const char __user *name = vma_get_anon_name(vma);
>> + struct mm_struct *mm = vma->vm_mm;
>> +
>> + unsigned long page_start_vaddr;
>> + unsigned long page_offset;
>> + unsigned long num_pages;
>> + unsigned long max_len = NAME_MAX;
>> + int i;
>> +
>> + page_start_vaddr = (unsigned long)name & PAGE_MASK;
>> + page_offset = (unsigned long)name - page_start_vaddr;
>> + num_pages = DIV_ROUND_UP(page_offset + max_len, PAGE_SIZE);
>> +
>> + seq_puts(m, "[anon:");
>> +
>> + for (i = 0; i < num_pages; i++) {
>> + int len;
>> + int write_len;
>> + const char *kaddr;
>> + long pages_pinned;
>> + struct page *page;
>> +
>> + pages_pinned = get_user_pages(current, mm, page_start_vaddr,
>> + 1, 0, 0, &page, NULL);
>> + if (pages_pinned < 1) {
>> + seq_puts(m, "<fault>]");
>> + return;
>> + }
>> +
>> + kaddr = (const char *)kmap(page);
>> + len = min(max_len, PAGE_SIZE - page_offset);
>> + write_len = strnlen(kaddr + page_offset, len);
>> + seq_write(m, kaddr + page_offset, write_len);
>> + kunmap(page);
>> + put_page(page);
>> +
>> + /* if strnlen hit a null terminator then we're done */
>> + if (write_len != len)
>> + break;
>> +
>> + max_len -= len;
>> + page_offset = 0;
>> + page_start_vaddr += PAGE_SIZE;
>> + }
>> +
>> + seq_putc(m, ']');
>> +}
>
> Again, sorry if this was already discussed...
>
> But for what? This moves the policy into the kernel and afaics buys nothing.
> Can't it simply print the number?
>
> If an application reads its own /proc/pid/maps, surely it knows how it should
> interpret the numeric values.
>
> If another process reads this file, and if it assumes that this number is a
> pointer into that task's memory, it can do sys_process_vm_readv() ?
I think there is value in keeping /proc/pid/maps human readable. A
userspace tool could certainly put together the same information, but
there would be no easy way to do it from the command line.
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