On Wed, Dec 11, 2013 at 12:26:17AM -0800, Joe Perches wrote:
On Wed, 2013-12-11 at 08:05 +0000, Al Viro wrote:
On Wed, Dec 11, 2013 at 07:55:26AM +0000, Al Viro wrote:
This sucker should return 0. Insufficiently large buffer will be handled by caller, TYVM, if you give that caller a chance to do so. Returning 1 from ->show() is a bug in almost all cases, and definitely so in this one.
Just in case somebody decides that above is worth copying: It Is Not. Original code is buggy, plain and simple. This one trades the older bug ("fail with -EINVAL whenever the buffer is too small") with just as buggy "silently skip an entry entirely whenever the buffer is too small".
Don't Do That.
Pardon - Joe has made seq_overflow return -1 instead of true. Correction to the above, then - s/This trades.*./This is just as buggy./
Yeah, I started to use true/false, 0/1, but thought I needed to match what seq_printf/seq_vprintf does.
Conclusion is still the same - Don't Do That. Returning -1 on insufficiently large buffer is a bug, plain and simple.
int seq_vprintf(struct seq_file *m, const char *f, va_list args) { int len;
if (m->count < m->size) { len = vsnprintf(m->buf + m->count, m->size - m->count, f, args); if (m->count + len < m->size) { m->count += len; return 0; } } seq_set_overflow(m); return -1; } EXPORT_SYMBOL(seq_vprintf);
int seq_printf(struct seq_file *m, const char *f, ...) { int ret; va_list args;
va_start(args, f); ret = seq_vprintf(m, f, args); va_end(args);
return ret; } EXPORT_SYMBOL(seq_printf);
And this patch series is completely misguided - it doesn't fix any bugs *and* it provides a misleading example for everyone. See the reaction right in this thread, proposing to spread the same bug to currently working iterators.
Anyway, changing seq_overflow is easy enough
You prefer this?
bool seq_overflow(struct seq_file *seq) { return m->count == m->size; }
I prefer a series that starts with fixing the obvious bugs (i.e. places where we return seq_printf/seq_puts/seq_putc return value from ->show()). All such places should return 0. Then we need to look at the remaining places that check return value of seq_printf() et.al. And decide whether the callers really care about it.
Theoretically, there is a legitimate case when we want to look at that return value. Namely, seq_print(...) if (!overflowed) do tons of expensive calculations generate more output return 0 That is the reason why those guys hadn't been returning void to start with. And yes, it was inviting bugs with ->show() returning -1 on overflows. Bad API design, plain and simple.
I'm not sure we actually have any instances of that legitimate case, TBH. _IF_ we do, we ought to expose seq_overflow() (with saner name - this one invites the same "it's an error, need to report it" kind of bugs) and use it in such places. But that needs to be decided on per-caller basis. And I'd expect that there would be few enough such places after we kill the obvious bugs.