usb-serial does not return read errors after disconnect

i noticed that while using minicom on a usb-serial device (PL2303), 
disconnecting it would make minicom spike using all the cpu.  looking into 
it, minicom does a simple select()/read() on the fd on the device, but those 
functions werent returning errors so it kept on looping.  a simple test 
program shows similar behavior: open a usb serial device, set the fd to 
nonblocking, and then in a loop just keep doing a read().  while the usb 
cable is plugged in, you get back the normal EAGAIN.  but when you unplug the 
device, read() just returns 0 rather than ENODEV or EIO.

i tried pokin around the usb-serial layer, but nothing obvious stands out.  
attached test case shows the issue: run it, watch the EAGAIN, and then unplug 
the device and watch no more output.
-mike

#include <errno.h>
#include <fcntl.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/stat.h>
#include <sys/types.h>

#define X(call) ({ \
		int _ret = call; \
		printf("%s = ", #call); \
		printf("%i\n", _ret); \
		_ret; \
	})

int hitit = 1;
void quitit(int sig)
{
	X(hitit = 0);
}

int main(int argc, char *argv[])
{
	const char *tty = (argc > 2 ? argv[2] : "/dev/ttyUSB0");
	int fd, ret;
	char buf[1024];

	setbuf(stdout, NULL);

	signal(SIGINT, quitit);

	fd = X(open(tty, O_RDONLY|O_NONBLOCK));

	while (hitit) {
		ret = X(read(fd, buf, sizeof(buf)));
		if (ret == -1)
			printf("\terrno = %i (%s)\n", errno, strerror(errno));
		sleep(1);
	}

	X(close(fd));

	return 0;
}

-------------------------------------------------------------------------
This SF.net email is sponsored by: Splunk Inc.
Still grepping through log files to find problems?  Stop.
Now Search log events and configuration files using AJAX and a browser.
Download your FREE copy of Splunk now >>  http://get.splunk.com/

_______________________________________________
[email protected]
To unsubscribe, use the last form field at:
https://lists.sourceforge.net/lists/listinfo/linux-usb-users

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v2.0.6 (GNU/Linux)
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=2u6L
-----END PGP SIGNATURE-----