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    SubjectRE: UDP recvmsg blocks after select(), 2.6 bug?
    Date
    > > This is a distraction. If the call to select() had been substituted
    > > with a call to recvmsg(), it would have blocked. Instead,
    > select() is
    > > returning 'yes, you can read', and then recvmsg() is blocking. The
    > > select() lied. The information is all sitting in the kernel packet
    >
    > No. A million things might happen between select() and recvmsg(), both
    > in kernel and application. For a consistent behaviour throughout all
    > possibilities, you *have* to assume that any read on a blocking fd may
    > block.

    Care to provide a real example?

    UDP isn't one. It was done for performance reasons as David admitted and it
    could very well be done otherwise: do the checksum before select returns.

    David has admitted the only reason Linux chose to do so is performance.

    It might be the case that a million things might happen between select and
    recvmsg, but none of them, as I can see, *have* to force Linux to work this
    way. The only reason as I can see is performance and imlementation
    convenience.

    Hua

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