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SubjectRe: [PATCH v2 1/1] misc: hpilo: switch .{read,write} ops to .{read,write}_iter
On Thu, Jul 14, 2022 at 01:54:52AM +0800, matt.hsiao@hpe.com wrote:
> From: Matt Hsiao <matt.hsiao@hpe.com>
>
> Commit 4d03e3cc59828c82ee89 ("fs: don't allow kernel reads and writes
> without iter ops") requested exclusive .{read,write}_iter ops for
> kernel_{read,write}. To support dependent drivers to access hpilo by
> kernel_{read,write}, switch .{read,write} ops to their iter variants.
>
> Signed-off-by: Matt Hsiao <matt.hsiao@hpe.com>

So this fixes a bug? What commit does this fix?

Should it go to stable branches? If so, which ones?

But my main question is I have no idea what the changelog means here.
What is a "dependent driver"? What does "exclusive" mean here? What is
a iter variant?



> ---
> drivers/misc/hpilo.c | 31 ++++++++++++++++++-------------
> 1 file changed, 18 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/misc/hpilo.c b/drivers/misc/hpilo.c
> index 8d00df9243c4..5d431a56b7eb 100644
> --- a/drivers/misc/hpilo.c
> +++ b/drivers/misc/hpilo.c
> @@ -23,6 +23,7 @@
> #include <linux/wait.h>
> #include <linux/poll.h>
> #include <linux/slab.h>
> +#include <linux/uio.h>
> #include "hpilo.h"
>
> static struct class *ilo_class;
> @@ -435,14 +436,14 @@ static void ilo_set_reset(struct ilo_hwinfo *hw)
> }
> }
>
> -static ssize_t ilo_read(struct file *fp, char __user *buf,
> - size_t len, loff_t *off)
> +static ssize_t ilo_read_iter(struct kiocb *iocb, struct iov_iter *to)
> {
> - int err, found, cnt, pkt_id, pkt_len;
> - struct ccb_data *data = fp->private_data;
> + int err = 0, found, cnt, pkt_id, pkt_len;
> + struct ccb_data *data = iocb->ki_filp->private_data;
> struct ccb *driver_ccb = &data->driver_ccb;
> struct ilo_hwinfo *hw = data->ilo_hw;
> void *pkt;
> + size_t len = iov_iter_count(to), copied;
>
> if (is_channel_reset(driver_ccb)) {
> /*
> @@ -477,7 +478,9 @@ static ssize_t ilo_read(struct file *fp, char __user *buf,
> if (pkt_len < len)
> len = pkt_len;
>
> - err = copy_to_user(buf, pkt, len);
> + copied = copy_to_iter(pkt, len, to);
> + if (unlikely(copied != len))

Why unlikely? If you can prove it is needed in benchmarks, great,
otherwise never add likely/unlikely as they are almost always wrong and
the compiler and cpu can do it better.


> + err = -EFAULT;
>
> /* return the received packet to the queue */
> ilo_pkt_enqueue(hw, driver_ccb, RECVQ, pkt_id, desc_mem_sz(1));
> @@ -485,14 +488,14 @@ static ssize_t ilo_read(struct file *fp, char __user *buf,
> return err ? -EFAULT : len;
> }
>
> -static ssize_t ilo_write(struct file *fp, const char __user *buf,
> - size_t len, loff_t *off)
> +static ssize_t ilo_write_iter(struct kiocb *iocb, struct iov_iter *from)
> {
> - int err, pkt_id, pkt_len;
> - struct ccb_data *data = fp->private_data;
> + int err = 0, pkt_id, pkt_len;
> + struct ccb_data *data = iocb->ki_filp->private_data;
> struct ccb *driver_ccb = &data->driver_ccb;
> struct ilo_hwinfo *hw = data->ilo_hw;
> void *pkt;
> + size_t len = iov_iter_count(from), copied;
>
> if (is_channel_reset(driver_ccb))
> return -ENODEV;
> @@ -506,9 +509,11 @@ static ssize_t ilo_write(struct file *fp, const char __user *buf,
> len = pkt_len;
>
> /* on failure, set the len to 0 to return empty packet to the device */
> - err = copy_from_user(pkt, buf, len);
> - if (err)
> + copied = copy_from_iter(pkt, len, from);
> + if (unlikely(copied != len)) {

Same here.

thanks,

greg k-h

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