On 2021/7/5 12:38, Viresh Kumar wrote:> On 05-07-21, 11:45, Jie Deng wrote: >> On 2021/7/5 10:40, Viresh Kumar wrote: >>> On 02-07-21, 16:46, Jie Deng wrote: >>> The right way of doing this is is making this function return - Error on failure >>> and 0 on success. There is no point returning number of successful additions >>> here. >> >> We need the number for virtio_i2c_complete_reqs to do cleanup. We don't have >> to >> >> do cleanup "num" times every time. Just do it as needed. > If you do full cleanup here, then you won't required that at the caller site. > >>> Moreover, on failures this needs to clean up (free the dmabufs) itself, just >>> like you did i2c_put_dma_safe_msg_buf() at the end. The caller shouldn't be >>> required to handle the error cases by freeing up resources. >> >> This function will return the number of requests being successfully prepared >> and make sure >> >> resources of the failed request being freed. And virtio_i2c_complete_reqs >> will free the >> >> resources of those successful request. > It just looks cleaner to give such responsibility to each and every function, > i.e. if they fail, they should clean stuff up instead of the caller. That's the > normal philosophy you will find across kernel in most of the cases. > >>>> + /* >>>> + * Condition (req && req == &reqs[i]) should always meet since >>>> + * we have total nr requests in the vq. >>>> + */ >>>> + if (!failed && (WARN_ON(!(req && req == &reqs[i])) || >>>> + (req->in_hdr.status != VIRTIO_I2C_MSG_OK))) >>> What about writing this as: >>> >>> if (!failed && (WARN_ON(req != &reqs[i]) || >>> (req->in_hdr.status != VIRTIO_I2C_MSG_OK))) >>> >>> We don't need to check req here since if req is NULL, we will not do req->in_hdr >>> at all. >> >> It's right here just because the &reqs[i] will never be NULL in our case. >> But if you see >> >> "virtio_i2c_complete_reqs" as an independent function, you need to check the >> >> req. From the perspective of the callee, you can't ask the caller always >> give you >> >> the non-NULL parameters. > We need to keep this driver optimized in its current form. If you see your own > argument here, then why don't you test vq or msgs for a valid pointer ? And even > reqs. > > If we know for certain that this will never happen, then it should be optimized. > But if you see a case where reqs[i] can be NULL here, then it would be fine. > ot the driver. And we don't need to take care of that.This is still not enough to convince me.? So I won't change them for now until I see it is the consensus of the majority. Thank you.
Viresh Kumar
2021-Jul-05 06:30 UTC
[PATCH v12] i2c: virtio: add a virtio i2c frontend driver
On 05-07-21, 14:22, Jie Deng wrote:> On 2021/7/5 12:38, Viresh Kumar wrote: > > On 05-07-21, 11:45, Jie Deng wrote: > > > On 2021/7/5 10:40, Viresh Kumar wrote: > > > > On 02-07-21, 16:46, Jie Deng wrote: > > > > The right way of doing this is is making this function return - Error on failure > > > > and 0 on success. There is no point returning number of successful additions > > > > here. > > > > > > We need the number for virtio_i2c_complete_reqs to do cleanup. We don't have > > > to > > > > > > do cleanup "num" times every time. Just do it as needed. > > If you do full cleanup here, then you won't required that at the caller site. > > > > > > Moreover, on failures this needs to clean up (free the dmabufs) itself, just > > > > like you did i2c_put_dma_safe_msg_buf() at the end. The caller shouldn't be > > > > required to handle the error cases by freeing up resources. > > > > > > This function will return the number of requests being successfully prepared > > > and make sure > > > > > > resources of the failed request being freed. And virtio_i2c_complete_reqs > > > will free the > > > > > > resources of those successful request. > > It just looks cleaner to give such responsibility to each and every function, > > i.e. if they fail, they should clean stuff up instead of the caller. That's the > > normal philosophy you will find across kernel in most of the cases. > > > > > + /* > > > > > + * Condition (req && req == &reqs[i]) should always meet since > > > > > + * we have total nr requests in the vq. > > > > > + */ > > > > > + if (!failed && (WARN_ON(!(req && req == &reqs[i])) || > > > > > + (req->in_hdr.status != VIRTIO_I2C_MSG_OK))) > > > > What about writing this as: > > > > > > > > if (!failed && (WARN_ON(req != &reqs[i]) || > > > > (req->in_hdr.status != VIRTIO_I2C_MSG_OK))) > > > > > > > > We don't need to check req here since if req is NULL, we will not do req->in_hdr > > > > at all. > > > > > > It's right here just because the &reqs[i] will never be NULL in our case. > > > But if you see > > > > > > "virtio_i2c_complete_reqs" as an independent function, you need to check the > > > > > > req. From the perspective of the callee, you can't ask the caller always > > > give you > > > > > > the non-NULL parameters. > > We need to keep this driver optimized in its current form. If you see your own > > argument here, then why don't you test vq or msgs for a valid pointer ? And even > > reqs. > > > > If we know for certain that this will never happen, then it should be optimized. > > But if you see a case where reqs[i] can be NULL here, then it would be fine. > > ot the driver. And we don't need to take care of that. > > > This is still not enough to convince me.? So I won't change them for now > until I see it > > is the consensus of the majority.Do you see reqs[i] to ever be NULL here ? If not, then if (req) is like if (true). Why would you want to have something like that ? -- viresh