Messages in this thread Patch in this message | | | Date | Fri, 15 Jul 2022 16:55:57 +0800 | From | Matt Hsiao <> | Subject | Re: [PATCH v2 1/1] misc: hpilo: switch .{read,write} ops to .{read,write}_iter |
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On Wed, Jul 13, 2022 at 08:28:24PM +0200, Greg KH wrote: > 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?
No, this is not a bug fix. Please see my explanation for your main question below.
> > Should it go to stable branches? If so, which ones?
No, it does not need to.
> > 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?
There is an out-of-box driver which is not in the upstream kernel yet that uses kernel_{read,write} to access the hpilo driver for talking to the iLO ASIC. Before commit 4d03e3cc59828c82ee89 ("fs: don't allow kernel reads and writes without iter ops"), kernel_{read,write} would call the .{read,write} file ops that hpilo already implemented, so there was no problem; But after that commit, kernel_{read,write} would only allow the .{read,write}_iter file ops, and disallowed the coexistence of .{read,write} file ops. Accessing hpilo now fails since it does not have the .{read,write}_iter file ops. To make it work, this patch implements the .{read,write}_iter file ops and removed the .{read,write} ones.
> > > > > --- > > 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.
Will remove it in the next verion of patch.
> > > > + 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.
Will remove it in the next verion of patch.
> > thanks, > > greg k-h
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