Re: Should applications close pcap_get_selectable_fd()?

[Michael Richardson <mcr () sandelman ca>]

Guy Harris <gharris () sonic net> wrote:
    > On Aug 13, 2026, at 4:22 PM, Mark Delany <fzx () xray emu st> wrote:

    >> This is probably more a documentation clarification than anything else as a light troll
    >> through the archives suggests the answer...
    >>
    >> pcap_fileno(3) is fairly explicit about suggesting that the returned fd is the same one as
    >> that used internally by pcap, however pcap_get_selectable_fd(3) is much less forthcoming
    >> on the matter.
    >>
    >> My naive reading is that pcap_get_selectable_fd() returns a unique fd for my own purposes
    >> and that I should close it when I'm done,

    > The documentation needs to be changed to make it clearer that it should
    > *not* be closed, because it could be, but is not guaranteed to be, the
    > same file descriptor as the one used for the capture mechanism. (Some
    > capture mechanism might require separate readable and selectable
    > FDs. Npcap requires the Windows equivalent - a HANDLE on which to do
    > reads, writes, and DeviceIoControl()s, and another HANDLE representing
    > an event that can be waited on.)

Should one call pcap_get_selectable_fd() before each call to select()/poll()
or are applications allowed to cache it?
I don't think any implementation would change it, but probably we should be
explicit about that too.

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