Messages in this thread |  | | Date | 6 Feb 2013 14:34:15 -0500 | From | "George Spelvin" <> | Subject | Re: [PATCH 3/4] pps: Use lookup list to reduce ldisc coupling |
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> Now that N_TTY uses tty->disc_data for its private data, > 'subclass' ldiscs cannot use ->disc_data for their own private data. > > Use a lookup list to associate the tty with the pps source.
Thanks for the cleanup. I fully agree my patch was not a good one; I just wanted someone more experienced to make the call on rearchitecting.
In particular, I was nervous about getting flamed by Linus for something that was too ambitious.
One thing I'd prefer to do would be to change:
+static struct pps_device *lookup_pps_by_tty(struct tty_struct *tty, + struct pps_data **p) +{ + unsigned long flags; + + spin_lock_irqsave(&pps_lock, flags); + list_for_each_entry((*p), &pps_list, link) { + if ((*p)->tty == tty) { + spin_unlock_irqrestore(&pps_lock, flags); + return (*p)->pps; + } + } + spin_unlock_irqrestore(&pps_lock, flags); + return NULL; +}
to:
static struct pps_data *lookup_pps_by_tty(struct tty_struct *tty) { unsigned long flags;
spin_lock_irqsave(&pps_lock, flags); list_for_each_entry(p, &pps_list, link) { if (p->tty == tty) break; } spin_unlock_irqrestore(&pps_lock, flags); return p; }
And do the data->pps dereferencing in the caller.
A more ambitious cleanup would use the existing pps_device list (maintained to allocate minor device numbers) and add an "owner" field that can be looked up on, without creating a new data structure and allocation.
(It could either be a generic "void *", or a "struct device *" and compare it to tty->dev.)
After all, despite the implementation effort to scale, the total number of pps devices in a system is usually at most 1 (I have a computer where I run 2, and I doubt there are many others on the planet who do that.)
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