[flashrom] [PATCH 5/7] Combine serialport_write and serialport_read into serialport_rw.

[Carl-Daniel Hailfinger]

Am 10.07.2013 21:21 schrieb Stefan Tauner:
> Because they share almost all code, combine them into serialport_rw
> and export the old functions as wrappers. This makes reads "empty reads"-
> aware and programmers able to detect such problems even on "blocking"
> reads. Also, this fixes error detection on Windows.
>
> Signed-off-by: Stefan Tauner <stefan.tauner at student.tuwien.ac.at>
> ---
>  serial.c | 83 ++++++++++++++++++++++++++++++----------------------------------
>  1 file changed, 39 insertions(+), 44 deletions(-)
>
> diff --git a/serial.c b/serial.c
> index 1b394cd..5f74fd1 100644
> --- a/serial.c
> +++ b/serial.c
> @@ -328,66 +330,59 @@ int serialport_shutdown(void *data)
>  	return 0;
>  }
>  
> -int serialport_write(unsigned char *buf, unsigned int writecnt)
> +#define EMPTY_TRIES 10

A total of 10 ms timeout is too fast for the Bus Pirate and some slower
serprog implementations AFAICS. I'd prefer a 1 s timeout before
signaling an error. That should be sufficient, and callers are supposed
to check for errors, so the 1 s timeout won't happen multiple times.


> +/* Writes (if \c outdir is true) or reads \c todo bytes from/into \c buf.
> + * Tries up to \c EMPTY_TRIES times with a timeout of \c ms ms between each try. */
> +static int serialport_rw(unsigned char *buf, unsigned int todo, bool outdir, unsigned int ms)
>  {
> -#ifdef _WIN32
> -	DWORD tmp = 0;
> -#else
> -	ssize_t tmp = 0;
> -#endif
> -	unsigned int empty_writes = 250; /* results in a ca. 125ms timeout */
> +	const char * const op = outdir ? "write" : "read";
> +	bool err = false;
> +	unsigned int empty_tries = EMPTY_TRIES;
>  
> -	while (writecnt > 0) {
> +	while (todo > 0) {
>  #ifdef _WIN32
> -		WriteFile(sp_fd, buf, writecnt, &tmp, NULL);
> +		DWORD cur = 0;
> +		if (outdir)
> +			err = !WriteFile(sp_fd, buf, todo, &cur, NULL);
> +		else
> +			err = !ReadFile(sp_fd, buf, todo, &cur, NULL);

Should we check for cur == 0 here? Can that happen?


>  #else
> -		tmp = write(sp_fd, buf, writecnt);
> -#endif
> -		if (tmp == -1) {
> -			msg_perr("Serial port write error!\n");
> +		ssize_t cur = 0;
> +		if (outdir)
> +			err = (cur = write(sp_fd, buf, todo)) < 0;

OK.


> +		else
> +			err = (cur = read(sp_fd, buf, todo)) < 0;

Should be <= 0 instead of < 0 AFAICS. See the POSIX man page of read():
"When attempting to read from an empty pipe or FIFO: If no process has
the pipe open for writing, read() shall return 0 to indicate end-of-file."

 
> +#endif
> +		if (err) {
> +			msg_perr("Serial port %s error!\n", op);
>  			return 1;
>  		}
> -		if (!tmp) {
> -			msg_pdbg2("Empty write\n");
> -			empty_writes--;
> -			programmer_delay(500);
> -			if (empty_writes == 0) {
> -				msg_perr("Serial port is unresponsive!\n");
> +		if (cur == 0) {
> +			msg_pdbg2("Empty %s.\n", op);
> +			empty_tries--;
> +			programmer_delay(ms * 1000);
> +			if (empty_tries == 0) {
> +				msg_perr("Serial port is unresponsive or disappeared!\n");
>  				return 1;
>  			}
> +			continue;
>  		}
> -		writecnt -= tmp;
> -		buf += tmp;
> +		todo -= cur;
> +		buf += cur;
> +		empty_tries = EMPTY_TRIES;
>  	}
>  
>  	return 0;
>  }
>  
> -int serialport_read(unsigned char *buf, unsigned int readcnt)
> +int serialport_write(unsigned char *buf, unsigned int writecnt)
>  {
> -#ifdef _WIN32
> -	DWORD tmp = 0;
> -#else
> -	ssize_t tmp = 0;
> -#endif
> -
> -	while (readcnt > 0) {
> -#ifdef _WIN32
> -		ReadFile(sp_fd, buf, readcnt, &tmp, NULL);
> -#else
> -		tmp = read(sp_fd, buf, readcnt);
> -#endif
> -		if (tmp == -1) {
> -			msg_perr("Serial port read error!\n");
> -			return 1;
> -		}
> -		if (!tmp)
> -			msg_pdbg2("Empty read\n");
> -		readcnt -= tmp;
> -		buf += tmp;
> -	}
> +	return serialport_rw(buf, writecnt, true, 1);
> +}
>  
> -	return 0;
> +int serialport_read(unsigned char *buf, unsigned int readcnt)
> +{
> +	return serialport_rw(buf, readcnt, false, 10);
>  }
>  
>  /* Tries up to timeout ms to read readcnt characters and places them into the array starting at c. Returns


Regards,
Carl-Daniel

-- 
http://www.hailfinger.org/