lkml.org 
[lkml]   [2004]   [Jan]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    Date
    From
    SubjectRe: [PATCH] bitmap parsing/printing routines, version 4
    Joe Korty wrote:
    > On Mon, Jan 19, 2004 at 01:17:26PM -0800, Matthew Dobson wrote:
    >
    >>Joe,
    >> I've attatched a small patch with some *small* changes, and the
    >>addition of a whole lotta comments. I'd like to see what you think.
    >>
    >>Changes:
    >>1) Added a missing '"' in the comment for the bitmap_parse function
    >>2) Renamed 'oc' to 'old_c' for readability
    >>3) Remove "totaldigits == 0" check at the end of bitmap_parse. I
    >>believe this check is redundant. The only way that totaldigits could be
    >>0 at the end of the function is if ndigits is also 0 (because they're
    >>both incremented at the same time), and this condition is already
    >>checked for at the end of each chunk parsed. Is this correct?
    >>
    >>Additions:
    >>4) A whole bunch of comments. Are these all correct?
    >>
    >>None of the things in my patch (with the possible exception of #3)
    >>change the functionality of the code, which looks great.
    >>
    >>Andrew, I agree with Paul's "thumbs-up" of Joe's patch. My patch is
    >>solely meant to increase the readability of the bitmap_parse function.
    >>
    >>Cheers!
    >>
    >>-Matt
    >
    >
    > Indeed you are correct, the final (totaldigits == 1) test can be removed.
    > Good catch.

    Thanks!

    > However, IMHO you added too many comments. Unlike Andrew, I do believe
    > one can have too many comments. Comments become 'too many' when they
    > dilute to the point that the code can no longer be clearly read.
    >
    > If you reduce the comments to just those that say something not easily
    > deduced from the code, then they would be acceptable to me, and would
    > make a useful addition IMO. That would be all but three, or perhaps four,
    > of them.
    >
    > Andrew, if you do like the fully commented version, then please remove
    > my name from the comment in the patch. The dilute style of coding is
    > not one I wish to have my name associated with.
    >
    > Thanks,
    > Joe

    I'm sorry you feel that way, Joe. I had no intention of "diluting" your
    code, and I certainly don't want you to remove your name from good code
    you spent significant time & effort on. I'm just about to go to sleep,
    so I made this patch pretty quickly. I think the 4 comments I kept are
    the most useful and non-obvious. Let me know if this looks acceptable
    to you. As I said, I have no desire to have you pull your name from the
    code, especially since I feel it is good code!

    Andrew, once Joe and I work out an acceptable patch, we'll make sure you
    get a copy.

    Cheers!

    -Matt
    --- linux-2.6.1-joe_korty-bitmap/lib/bitmap.c.orig Mon Jan 19 11:45:32 2004
    +++ linux-2.6.1-joe_korty-bitmap/lib/bitmap.c Mon Jan 19 22:57:19 2004
    @@ -209,13 +209,13 @@ EXPORT_SYMBOL(bitmap_snprintf);
    * bits of the resultant bitmask. No chunk may specify a value larger
    * than 32 bits (-EOVERFLOW), and if a chunk specifies a smaller value
    * then leading 0-bits are prepended. -EINVAL is returned for illegal
    - * characters and for grouping errors such as "1,,5", ,44", "," and "".
    + * characters and for grouping errors such as "1,,5", ",44", "," and "".
    * Leading and trailing whitespace accepted, but not embedded whitespace.
    */
    int bitmap_parse(const char __user *ubuf, unsigned int ubuflen,
    unsigned long *maskp, int nmaskbits)
    {
    - int i, c, oc, ndigits, totaldigits, nchunks, nbits;
    + int i, c, old_c, totaldigits, ndigits, nchunks, nbits;
    u32 chunk;

    bitmap_clear(maskp, nmaskbits);
    @@ -223,21 +223,39 @@ int bitmap_parse(const char __user *ubuf
    nchunks = nbits = totaldigits = c = 0;
    do {
    chunk = ndigits = 0;
    +
    + /* Get the next chunk of the bitmap */
    while (ubuflen) {
    - oc = c;
    + old_c = c;
    if (get_user(c, ubuf++))
    return -EFAULT;
    ubuflen--;
    if (isspace(c))
    continue;
    - if (totaldigits && c && isspace(oc))
    +
    + /*
    + * If the last character was a space and the current
    + * character isn't '\0', we've got embedded whitespace.
    + * This is a no-no, so throw an error.
    + */
    + if (totaldigits && c && isspace(old_c))
    return -EINVAL;
    - if (!c || c == ',')
    +
    + /* A '\0' or a ',' signal the end of the chunk */
    + if (c == '\0' || c == ',')
    break;
    +
    if (!isxdigit(c))
    return -EINVAL;
    +
    + /*
    + * Make sure there are at least 4 free bits in 'chunk'.
    + * If not, this hexdigit will overflow 'chunk', so
    + * throw an error.
    + */
    if (chunk & ~((1UL << (CHUNKSZ - 4)) - 1))
    return -EOVERFLOW;
    +
    chunk = (chunk << 4) | unhex(c);
    ndigits++; totaldigits++;
    }
    @@ -245,6 +263,7 @@ int bitmap_parse(const char __user *ubuf
    return -EINVAL;
    if (nchunks == 0 && chunk == 0)
    continue;
    +
    bitmap_shift_right(maskp, maskp, CHUNKSZ, nmaskbits);
    for (i = 0; i < CHUNKSZ; i++)
    if (chunk & (1 << i))
    @@ -255,8 +274,6 @@ int bitmap_parse(const char __user *ubuf
    return -EOVERFLOW;
    } while (ubuflen && c == ',');

    - if (totaldigits == 0)
    - return -EINVAL;
    return 0;
    }
    EXPORT_SYMBOL(bitmap_parse);
    \
     
     \ /
      Last update: 2005-03-22 14:00    [W:0.028 / U:157.552 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site