Re: [PATCH v2 2/2] pcapng: check if writev() returns a partial write

["Mário Kuka" <kuka@cesnet.cz>]

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> Since this is being written to a file, handling partial writes makes little
> sense. The only case where partial write would happen would be if filesystem
> was full. Retrying just adds unnecessary complexity.
>
> If you really want to track this, then add a dropped counter.

But the file descriptor doesn't have to refer to just a regular file, what
if it's a socket or a pipe or some device? The pcapng documentation doesn't
say anything about any restrictions, so the implementation should be fully
generic. What's the point of a function to write packets to a file 
descriptor
where there's a risk that it won't write all the packets or that the 
file will
by corrupted due to a partial write and still not even let me know about 
it?

On 29/07/2022 18:00, Stephen Hemminger wrote:
> On Fri, 29 Jul 2022 09:18:41 +0200
> Mário Kuka <kuka@cesnet.cz> wrote:
>
>> +pcapng_writev(int fd, struct iovec *iov, const int count)
>> +{
>> +	size_t total = 0;
>> +	int at = 0;
>> +
>> +	while (at < count) {
>> +		/*
>> +		 * Note: writev() can return the following on a write request:
>> +		 *     Complete:
>> +		 *         written = [sum of all iov.iov_len]
>> +		 *     Partial:
>> +		 *         written < [sum of all iov.iov_len]
>> +		 *     Deferred:
>> +		 *         written = -1, errno = [EAGAIN]
>> +		 *
>> +		 * Partial and deferred writes are only possible with O_NONBLOCK set.
>> +		 *
>> +		 * If we get a partial result, we have to call the writev() again on any ivo buffers
>> +		 * that have not been fully written.
>> +		 */
>> +		ssize_t written = writev(fd, &iov[at], count - at);
>> +		if (unlikely(written < 0))
>> +			return written;
>> +
>> +		total += written;
>> +		at += pcapng_update_iov(&iov[at], count - at, written);
>> +	}
>> +
>> +	return total;
> Since this is being written to a file, handling partial writes makes little
> sense. The only case where partial write would happen would be if filesystem
> was full. Retrying just adds unnecessary complexity.
>
> If you really want to track this, then add a dropped counter.


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