Re: [PATCH V2] fs_parser: remove fs_parameter_description name field

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

On Thu, Dec 19, 2019 at 11:29:51PM +0000, Al Viro wrote:

> I wonder if we should do the following:
> 	* structure with two members - pointer to fc_log and a string
> (prefix) embedded into fs_context, in place of ->log.
> 	* __logfc() taking pointer to that struct, integer or
> character representing the "log level", then format and vararg part.
> 	* warnf() being simply __logfc(&fc->log, 'w', fmt, ## __VA_ARGS__)
> 	* __logfc() using "%c %s%s%pV",
> 				loglevel,
> 				prefix?prefix:"",
> 				prefix ? ":" : "",
> 				fmt, va
> for kvasprintf() (assuming that %pV *can* be used with it, of course)
> 	* const char *set_log_prefix(pointer, string) replacing the
> prefix field of the struct and returning the original.  fs_context
> allocation would set it to fs_type->name.
> 	* __fs_parse() would be taking a pointer to that field of
> fs_context instead of the entire thing; ditto for fs_param_is_...()
> 	* rbd would create a local structure with "rbd" for prefix
> and NULL for log
> 	* net/ceph would replace the prefix in the thing it has
> been given with "libceph" and revert back to original in the end
> 
> The most worrying part in that is kvasprintf interplay with %pV -
> we might need to open-code it, since we need va_copy() not of that
> sucker's arguments, but of the va_list one level deeper.

We won't - va_format() itself does take a copy.  So no open-coding
is needed, kasprint() would work.  OK, that simplifies things...