[systemd-devel] [PATCH] util: arg 'nbytes' of loop_read/write should be of type ssize_t

[Kay Sievers]

On Tue, May 3, 2011 at 03:00, fykcee1 at gmail.com <fykcee1 at gmail.com> wrote:
> 2011/5/3 Kay Sievers <kay.sievers at vrfy.org>
>>
>> On Mon, May 2, 2011 at 05:18, fykcee1 at gmail.com <fykcee1 at gmail.com> wrote:
>> >  loop_read/write will try to fill/read 'nbytes' of caller supplying buffer.
>> > This argument is currently of type size_t, which is always true
>> > for loop quit condition "while (nbytes > 0)", hence we change it to
>> > type ssize_t here.
>>
>> Where would that be useful? It's the size of the buffer supplied to
>> the function, just like read() itself has.
> Note "while(nbytes > 0)" is equal to "while(true)"

Why? nbytes can be zero, and then it's false. It's counting down with
every read().

> if the supplying
> buffer is smaller than contents of a file, read syscall may overwrite
> memory after 'buf', or return with errno EFAULT.

How, when p moves forward, and nbytes counts down to zero?

>> > This also helps to detect passed-in 'nbytes' of value -1
>> > for example.
>>
>> Detect what that way, a negative sizeof()?
> This 'nbytes' maybe a variable, and happens to be -1?

No, it can't. Why would it?

> Also, it is
> symmetric if the range of return value(number of bytes read) is equal
> to the range of 'nbytes'.

But nbytes is a size of a buffer, just like the native read() has.
What has it to do with a return value of a function that can be
negative too? There is never anything returned, it's only ever passed
in, it's just a size parameter.

Kay