On Thu, Oct 09, 2014 at 10:57:06AM +1100, NeilBrown wrote: > To match the previous patch which used the pre-alloc buffer for > writes, this patch causes reads to use the same buffer. > This is not strictly necessary as the current seq_read() will allocate > on first read, so user-space can trigger the required pre-alloc. But > consistency is valuable. > > The read function is somewhat simpler than seq_read() and, for example, > does not support reading from an offset into the file: reads must be > at the start of the file. > > As seq_read() does not use the prealloc buffer, ->seq_show is > incompatible with ->prealloc and caused an EINVAL return from open(). > sysfs code which calls into kernfs always chooses the correct function. > > As the buffer is shared with writes and other reads, the mutex is > extended to cover the copy_to_user. > > Signed-off-by: NeilBrown <[email protected]>
Reviewed-by: Tejun Heo <[email protected]> Some nitpicks. > @@ -690,6 +694,12 @@ static int kernfs_fop_open(struct inode *inode, struct > file *file) > */ > of->atomic_write_len = ops->atomic_write_len; > > + error = -EINVAL; > + if (ops->prealloc && ops->seq_show) > + /* ->seq_show is incompatible with ->prealloc, > + * ->read must be used instead. > + */ > + goto err_free; Let's please use fully-winged comments. If it looks weird inside the if block, it can just be located right on top, I think. Also, wouldn't it be better if the comment explained the reason for the incompatibility? Along the same line, I think it'd be better if this is also explicitly explained where ->prealloc is defined. > +/* kernfs read callback for regular sysfs files with pre-alloc */ > +static ssize_t sysfs_kf_read(struct kernfs_open_file *of, char *buf, > + size_t count, loff_t pos) > +{ > + const struct sysfs_ops *ops = sysfs_file_ops(of->kn); > + struct kobject *kobj = of->kn->parent->priv; > + > + if (pos || buf != of->prealloc_buf) > + /* If buf != of->prealloc_buf, we don't know how > + * large it is, so cannot safely pass it to ->show > + */ > + return 0; > + return ops->show(kobj, of->kn->priv, buf); > +} Ditto on the comment formatting also shouldn't the latter condition be a WARN_ON_ONCE()? Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
