Date: Mon, 27 May 2019 23:21:50 +0300 From: Andriy Gapon <avg@FreeBSD.org> To: "Bjoern A. Zeeb" <bzeeb-lists@lists.zabbadoz.net> Cc: freebsd-arch@FreeBSD.org Subject: Re: proposal: require ivar accessors to succeed Message-ID: <f489acfb-c107-82d1-8d01-19f36a78d1c4@FreeBSD.org> In-Reply-To: <E7700915-34BE-4371-A258-C010638CFA38@lists.zabbadoz.net> References: <2b2ab28f-45c5-1c28-f923-170d95c20c3d@FreeBSD.org> <E7700915-34BE-4371-A258-C010638CFA38@lists.zabbadoz.net>
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On 27/05/2019 21:10, Bjoern A. Zeeb wrote: > On 27 May 2019, at 5:44, Andriy Gapon wrote: > >> __BUS_ACCESSOR() macro is used to define accessors to bus IVAR variables. >> Unfortunately, accessors defined in such a fashion completely ignore return >> values of BUS_READ_IVAR() and BUS_WRITE_IVAR() method calls. There is no way to >> see if a call is successful. Typically, this should not be a problem as a >> device driver targets a specific bus (sometimes, buses) and it should know what >> IVARs the bus has. So, the driver should make only those IVAR calls that are >> supposed to always succeed on the bus. >> But sometimes things can go wrong as with everything else. >> >> So, I am proposing to add some code to __BUS_ACCESSOR to verify the success. >> For example, we can panic when a call fails. The checks could be under >> INVARIANTS or under DIAGNOSTICS or under a new kernel option. >> A less drastic option is to print a warning message on an error. >> >> This is mostly intended to help driver writers and maintainers. >> >> Opinions, suggestions, etc are welcome. > > What about “fixing” the KPI (possibly adding a 2nd one), deprecating the old > one, and (slowly over time) migrating old stuff over? I think that the two proposals are not mutually exclusive. And I think that both make sense. However, it's hard for me to imagine a desire to replace code like this devid = pci_get_devid(dev); with this err = pci_get2_devid(dev, &devid); if (err != 0) { ... } Especially given that, modulo bugs, dev is going to be a device on the pci bus and the call is going to succeed. In other words, in my opinion, the only cases where an accessor is allowed to fail are: - a driver somehow attached to a device on an unexpected bus - uncoordinated changes in between a bus driver and a device driver So, programming errors. -- Andriy Gapon
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