On Tue 10-04-18 19:56:14, Rasmus Villemoes wrote:
> Here's an idea that does require rewriting all the existing
> reiserfs_warning etc. calls, but avoids all the fragile vararg handling
> and adds proper compile-time format string checking:
>
> Have reiserfs_warning (and friends) be a macro that expands to
>
> reiserfs_printf_start();
> __reiserfs_warning(the arguments);
> reiserfs_printf_stop();
>
> where printf_start would take a spinlock and reset some bookkeeping
> variables. Then all the sprintf_de_head etc. helpers would have a
> prototype like
>
> const char *sprintf_de_head(struct reiserfs_de_head *deh)
>
> and they would print their output to the current error_buf, updating the
> above-mentioned bookkeeping variable(s) and return a pointer to the
> start of the area they printed to. So
>
> reiserfs_warning("bla %a", deh)
>
> would get changed to
>
> reiserfs_warning("bla %s", sprintf_de_head(deh))
>
> Basically, the current error_buf would only be used for holding the
> result of the custom specifiers, everything else goes directly to
> printk's output buffer, so no need to make error_buf larger (a single
> printk is limited to 1024 bytes anyway...), and fmt_buf goes away
> completely. That reduction in static footprint should make up for at
> least some of the bloat caused by the extra code the new
> reiserfs_warning would generate. Also, I don't think this should make us
> hold the spinlock (much) longer than is currently the case, and
> trivially solves the problem of not actually holding the spinlock when
> passing the error_buf to printk.
So I don't see how this would work for more complex warnings like:
reiserfs_warning("bla %*d foo %a bar %llx %a", width, number, deh,
another_number, deh2)
Either we'd need some macro magic rewriting 'deh' and 'deh2' arguments to
sprintf_de_head(deh) and sprintf_de_head(deh2) (which I don't see how we
could do), rewrite the whole format string and then pass it to vsnprintf()
or I don't see how we could get away without knowing how much from va_list
vsnprinf() consumed...
Honza
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
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