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    SubjectRe: [PATCH 14/44] kdbus: Simplify expression in kdbus_get_memfd()
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    Hi

    On Thu, Oct 8, 2015 at 1:31 PM, Sergei Zviagintsev <sergei@s15v.net> wrote:
    > '(s & m) != m' means that mask 'm' contains some bits which are not set
    > in 's', and this is literally equal to '~s & m'.

    Sure, but you make the code look much less obvious. Checking a bit is
    set is "a & b", checking if not set is "!(a & b)". If you check
    whether a whole mask is set, you run "(a & m) == m", checking whether
    it not set should be the negation, which is "(a & m) != m".

    I'd prefer keeping the current code, unless the compiler cannot figure
    it out on its own.
    David

    > Signed-off-by: Sergei Zviagintsev <sergei@s15v.net>
    > ---
    > ipc/kdbus/message.c | 2 +-
    > 1 file changed, 1 insertion(+), 1 deletion(-)
    >
    > diff --git a/ipc/kdbus/message.c b/ipc/kdbus/message.c
    > index ae565cd343f8..c7ef23d40471 100644
    > --- a/ipc/kdbus/message.c
    > +++ b/ipc/kdbus/message.c
    > @@ -273,7 +273,7 @@ static struct file *kdbus_get_memfd(const struct kdbus_memfd *memfd)
    > s = shmem_get_seals(f);
    > if (s < 0)
    > ret = ERR_PTR(-EMEDIUMTYPE);
    > - else if ((s & m) != m)
    > + else if (~s & m)
    > ret = ERR_PTR(-ETXTBSY);
    > else if (memfd->start + memfd->size > (u64)i_size_read(file_inode(f)))
    > ret = ERR_PTR(-EFAULT);
    > --
    > 1.8.3.1
    >


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