On 09/18/2013 06:04 AM, David Howells wrote:
Joe Perches <joe@xxxxxxxxxxx> wrote:
On Tue, 2013-09-17 at 18:08 -0500, danielfsantos@xxxxxxx wrote:
This adds an extension for the integral format specifier suffix of 'e',
so that the format %[duxXo]e will result in printing an number (as
before) in addition to a name and descrption for an error code, if such
support is enabled and a name and descrption is found.
My initial thought was to use the glibc extension of '%m', but this
format specifier uses the value of libc's errno and adding a value
breaks gcc's printf parsing. I'm not convinced that the 'e' extension
is optimal, although there are only four instances of this pattern in
the kernel that would need to be changed.
git grep -E '".*%[#0\ +\-]*[0-9]*[hljzt]*[idoxXu]e'
Alternatively, 'E' was another thought for a suffix as well.
I'd much rather see another %p extension used instead
of generating odd output given normal printf formats.
%pE might work
I guess you'd use that with ERR_PTR(). On one hand, it would look decidedly
odd, but on the other hand, we have errors in pointers in a lot of places
already which wouldn't then need converting back - so it doesn't seem entirely
unreasonable.
David
Hmm, this discussion makes me pine for the gnu libc '%m' extension even
further. I wish there was an easy way to tell gcc that you want it to
check your format, but here are my extensions. Oh well.
Honestly, I'm not too keen on the %pE idea, although I can see that %p
is where all of the kernel extensions currently are. Unless I'm
incorrect, if I use ERR_PTR() on a signed int on a x86_64 where pointer
is 64 bits and int is 32, wouldn't that mean a signed conversion
instruction where the sign bit has to be moved from bit 31 to 63?
Either way, %pE does seem to make a lot of sense for conditions where we
already have a pointer that we would otherwise use PTR_ERR() to convert,
but it just seems klunky to use it on an int, to have it treated like a
pointer and then re-interpreted as an int. Maybe we can add %pE as well
as %dE and leave [ioxXu] out of it?
Daniel
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