• Masatake YAMATO's avatar
    check ADVICE of fadvise64_64 even if get_xip_page is given · b5beb1ca
    Masatake YAMATO authored
    I've written some test programs in ltp project.  During writing I met an
    problem which I cannot solve in user land.  So I wrote a patch for linux
    kernel.  Please, include this patch if acceptable.
    
    The test program tests the 4th parameter of fadvise64_64:
    
        long sys_fadvise64_64(int fd, loff_t offset, loff_t len, int advice);
    
    My test case calls fadvise64_64 with invalid advice value and checks errno is
    set to EINVAL.  About the advice parameter man page says:
    
        ...
        Permissible values for advice include:
    
    	   POSIX_FADV_NORMAL
                      ...
    	   POSIX_FADV_SEQUENTIAL
                      ...
    	   POSIX_FADV_RANDOM
    		  ...
    	   POSIX_FADV_NOREUSE
                      ...
    	   POSIX_FADV_WILLNEED
                      ...
    	   POSIX_FADV_DONTNEED
    		  ...
        ERRORS
               ...
    	   EINVAL An invalid value was specified for advice.
    
    However, I got a bug report that the system call invocations
    in my test case returned 0 unexpectedly.
    
    I've inspected the kernel code:
    
        asmlinkage long sys_fadvise64_64(int fd, loff_t offset, loff_t len, int advice)
        {
    	    struct file *file = fget(fd);
    	    struct address_space *mapping;
    	    struct backing_dev_info *bdi;
    	    loff_t endbyte;			/* inclusive */
    	    pgoff_t start_index;
    	    pgoff_t end_index;
    	    unsigned long nrpages;
    	    int ret = 0;
    
    	    if (!file)
    		    return -EBADF;
    
    	    if (S_ISFIFO(file->f_path.dentry->d_inode->i_mode)) {
    		    ret = -ESPIPE;
    		    goto out;
    	    }
    
    	    mapping = file->f_mapping;
    	    if (!mapping || len < 0) {
    		    ret = -EINVAL;
    		    goto out;
    	    }
    
    	    if (mapping->a_ops->get_xip_page)
    		    /* no bad return value, but ignore advice */
    		    goto out;
        ...
        out:
    	    fput(file);
    	    return ret;
        }
    
    I found the advice parameter is just ignored in the case
    mapping->a_ops->get_xip_page is given. This behavior is different from
    what is written on the man page. Is this o.k.?
    
    get_xip_page is given if CONFIG_EXT2_FS_XIP is true.
    Anyway I cannot find the easy way to detect get_xip_page
    field is given or CONFIG_EXT2_FS_XIP is true from the
    user space.
    
    I propose the following patch which checks the advice parameter
    even if get_xip_page is given.
    Signed-off-by: default avatarMasatake YAMATO <yamato@redhat.com>
    Acked-by: default avatarCarsten Otte <cotte@de.ibm.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    b5beb1ca
fadvise.c 2.86 KB