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    SubjectRe: [PATCH] Chardev checking of overlapping ranges is incorrect.
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    On Mon, Aug 07, 2006 at 05:55:55PM -0500, linas wrote:
    >
    > The current code in register_chrdev_region() attempts to check

    A debug printk escaped with that patch. Here's the proper patch.
    --linas

    [PATCH] Chardev checking of overlapping ranges is incorrect.

    The current code in register_chrdev_region() attempts to check
    for overlapping regions of minor device numbers, but performs
    that check incorrectly. For example, if a device with minor
    numbers 128, 129, 130 is registered first, and a device with
    minor number 3,4,5 is registered later, then the later range
    is incorrectly identified as "overlapping" (since 130>3),
    when clearly this is the wrong conclusion.

    This patch fixes the overlap check to work correctly.

    Signed-off-by: Signed-off-by: Linas Vepstas <linas@austin.ibm.com>

    ----
    fs/char_dev.c | 8 ++++++--
    1 file changed, 6 insertions(+), 2 deletions(-)

    Index: linux-2.6.18-rc3-mm2/fs/char_dev.c
    ===================================================================
    --- linux-2.6.18-rc3-mm2.orig/fs/char_dev.c 2006-08-07 17:16:53.000000000 -0500
    +++ linux-2.6.18-rc3-mm2/fs/char_dev.c 2006-08-07 17:57:51.000000000 -0500
    @@ -113,9 +113,13 @@ __register_chrdev_region(unsigned int ma
    (((*cp)->baseminor >= baseminor) ||
    ((*cp)->baseminor + (*cp)->minorct > baseminor))))
    break;
    +
    + /* Check for overlap of minor ranges */
    if (*cp && (*cp)->major == major &&
    - (((*cp)->baseminor < baseminor + minorct) ||
    - ((*cp)->baseminor + (*cp)->minorct > baseminor))) {
    + ((((*cp)->baseminor <= baseminor) &&
    + ((*cp)->baseminor + (*cp)->minorct >= baseminor)) ||
    + (((*cp)->baseminor >= baseminor) &&
    + ((*cp)->baseminor <= baseminor+minorct)))) {
    ret = -EBUSY;
    goto out;
    }
    -
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