Re: [PATCH bpf-next v2 1/6] kallsyms: Add KALLSYMS_QUERY ioctl to /proc/kallsyms

[David Laight <david.laight.linux@gmail.com>]

On Wed, 4 Nov 2026 16:05:52 -0800
Samuel Wu <wusamuel@google.com> wrote:

> > I think it might be more sensible (less pitfalls later on) to return
> > the symbol number - not that of the next one.  
> 
> What pitfalls were you anticipating? If the current symbol's position
> is returned, userspace needs another ioctl() call and an -ENOENT
> check, to learn that there are no more matches. Alternatively,
> returning the next position means every call pays for a look-ahead,
> which for an unfiltered query walks the module symbols even when
> userspace only wants the first match.

I was thinking more of the kernel api.
The 'position' is just an array index.
So a 'read by symbol name' would return the array index of that symbol.
A 'read by symbol name index' would return the name (uncompressed) and
do the lookup (binary search and linear scan) to find the value.

I've used a bit in the 'sorted by name array' to indicate that the
symbol is a duplicate of the previous one.
So checking an 'exact match' for being a duplicate is cheap.
But for a partial match you start needing the name buffer to be in-out
on the read-by position request.
So you start needing 'read by position' and 'read by position with
name compare'.
It is likely that the caller will need to validate the name anyway. 

An 'interesting' idea would be an ioctl that returned the value of
the nth symbol along with the name of the n+1th.
That might get confusing though.

David


> 
> Andrii, do you have a preference between the two?