Re: Blocking read() from a USB->Serial adapter.

On 2006-11-25, Floyd L. Davidson <floyd@xxxxxxxxxx> wrote:

Or until the driver decides to return for whatever reason it
chooses. On success, you're guaranteed a minimum of one byte.

Maybe. (Maybe not too!)

There's the case where the file is at EOF. Is there another
case where read() will return success with 0 bytes?

Any time there is no data available. With a file that will
indeed set the EOF flag, but with a serial port (or a pipe, or a
console) there is no such concept.

Sure there is. The tty line discipline will generate an "EOF"
condition and return 0 bytes when it sees the EOF character
(typically ctrl-d) as the first byte after read() is called.

If the timer is enabled, and times out, read() will return 0.

You're right. I thought it returned with an ETIMEDOUT error,
but I was probably thinking of a different OS.

Another possibility is if the number of bytes request was 0,
read() will return 0.

Yup -- I forgot about that.

--
Grant Edwards
grante@xxxxxxxx
.

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