Re: [PATCH 1/6] VFS: improve interface for lookup_one functions

[Al Viro <viro@zeniv.linux.org.uk>]

On Thu, Mar 20, 2025 at 02:04:49PM +0000, David Howells wrote:
> NeilBrown <neil@brown.name> wrote:
> 
> > Also the path component name is passed as "name" and "len" which are
> > (confusingly?) separate by the "base".  In some cases the len in simply
> > "strlen" and so passing a qstr using QSTR() would make the calling
> > clearer.
> > Other callers do pass separate name and len which are stored in a
> > struct.  Sometimes these are already stored in a qstr, other times it
> > easily could be.
> > 
> > So this patch changes these three functions to receive a 'struct qstr',
> > and improves the documentation.
> 
> You did want 'struct qstr' not 'struct qstr *' right?  I think there are
> arches where this will cause the compiler to skip a register argument or two
> if it's the second argument or third argument - i386 for example.  Plus you
> have an 8-byte alignment requirement because of the u64 in it that may suck if
> passed through several layers of function.

Not just that - you end up with *two* struct qstr instances for no good reason,
copying from the one passed by value field-by-field into the other one, then
passing the *address* of the copy to the functions that do actual work.