msync.c

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/*
 *  linux/mm/msync.c
 *
 * Copyright (C) 1994-1999  Linus Torvalds
 */

/*
 * The msync() system call.
 */
#include <linux/fs.h>
#include <linux/mm.h>
#include <linux/mman.h>
#include <linux/file.h>
#include <linux/syscalls.h>
#include <linux/sched.h>

/*
 * MS_SYNC syncs the entire file - including mappings.
 *
 * MS_ASYNC does not start I/O (it used to, up to 2.5.67).
 * Nor does it marks the relevant pages dirty (it used to up to 2.6.17).
 * Now it doesn't do anything, since dirty pages are properly tracked.
 *
 * The application may now run fsync() to
 * write out the dirty pages and wait on the writeout and check the result.
 * Or the application may run fadvise(FADV_DONTNEED) against the fd to start
 * async writeout immediately.
 * So by _not_ starting I/O in MS_ASYNC we provide complete flexibility to
 * applications.
 */
SYSCALL_DEFINE3(msync, unsigned long, start, size_t, len, int, flags)
{
    unsigned long end;
    struct mm_struct *mm = current->mm;
    struct vm_area_struct *vma;
    int unmapped_error = 0;
    int error = -EINVAL;

    if (flags & ~(MS_ASYNC | MS_INVALIDATE | MS_SYNC))
        goto out;
    if (start & ~PAGE_MASK)
        goto out;
    if ((flags & MS_ASYNC) && (flags & MS_SYNC))
        goto out;
    error = -ENOMEM;
    len = (len + ~PAGE_MASK) & PAGE_MASK;
    end = start + len;
    if (end < start)
        goto out;
    error = 0;
    if (end == start)
        goto out;
    /*
     * If the interval [start,end) covers some unmapped address ranges,
     * just ignore them, but return -ENOMEM at the end.
     */
    down_read(&mm->mmap_sem);
    vma = find_vma(mm, start);
    for (;;) {
        struct file *file;

        /* Still start < end. */
        error = -ENOMEM;
        if (!vma)
            goto out_unlock;
        /* Here start < vma->vm_end. */
        if (start < vma->vm_start) {
            start = vma->vm_start;
            if (start >= end)
                goto out_unlock;
            unmapped_error = -ENOMEM;
        }
        /* Here vma->vm_start <= start < vma->vm_end. */
        if ((flags & MS_INVALIDATE) &&
                (vma->vm_flags & VM_LOCKED)) {
            error = -EBUSY;
            goto out_unlock;
        }
        file = vma->vm_file;
        start = vma->vm_end;
        if ((flags & MS_SYNC) && file &&
                (vma->vm_flags & VM_SHARED)) {
            get_file(file);
            up_read(&mm->mmap_sem);
            error = vfs_fsync(file, 0);
            fput(file);
            if (error || start >= end)
                goto out;
            down_read(&mm->mmap_sem);
            vma = find_vma(mm, start);
        } else {
            if (start >= end) {
                error = 0;
                goto out_unlock;
            }
            vma = vma->vm_next;
        }
    }
out_unlock:
    up_read(&mm->mmap_sem);
out:
    return error ? : unmapped_error;
}