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;
}
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