* [PATCH v2] /dev/zero: also implement ->read
@ 2020-09-07 7:51 Christoph Hellwig
2020-09-07 8:21 ` Greg KH
0 siblings, 1 reply; 4+ messages in thread
From: Christoph Hellwig @ 2020-09-07 7:51 UTC (permalink / raw)
To: arnd, gregkh; +Cc: linux-kernel, Christophe Leroy
Christophe reported a major speedup due to avoiding the iov_iter
overhead, so just add this trivial function.
Suggested-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Tested-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
Changes since v1:
- fix the Suggested-by: tag
- report the actually read bytes in case of a partial clear_user
- remove an impossible to hit conditional
drivers/char/mem.c | 28 ++++++++++++++++++++++++++++
1 file changed, 28 insertions(+)
diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index abd4ffdc8cdebc..94c2b556cf9728 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -726,6 +726,33 @@ static ssize_t read_iter_zero(struct kiocb *iocb, struct iov_iter *iter)
return written;
}
+static ssize_t read_zero(struct file *file, char __user *buf,
+ size_t count, loff_t *ppos)
+{
+ size_t cleared = 0;
+
+ while (count) {
+ size_t chunk = min_t(size_t, count, PAGE_SIZE);
+ size_t left;
+
+ left = clear_user(buf + cleared, chunk);
+ if (unlikely(left)) {
+ cleared += (chunk - left);
+ if (!cleared)
+ return -EFAULT;
+ break;
+ }
+ cleared += chunk;
+ count -= chunk;
+
+ if (signal_pending(current))
+ break;
+ cond_resched();
+ }
+
+ return cleared;
+}
+
static int mmap_zero(struct file *file, struct vm_area_struct *vma)
{
#ifndef CONFIG_MMU
@@ -921,6 +948,7 @@ static const struct file_operations zero_fops = {
.llseek = zero_lseek,
.write = write_zero,
.read_iter = read_iter_zero,
+ .read = read_zero,
.write_iter = write_iter_zero,
.mmap = mmap_zero,
.get_unmapped_area = get_unmapped_area_zero,
--
2.28.0
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH v2] /dev/zero: also implement ->read
2020-09-07 7:51 [PATCH v2] /dev/zero: also implement ->read Christoph Hellwig
@ 2020-09-07 8:21 ` Greg KH
2020-09-07 8:21 ` Christoph Hellwig
0 siblings, 1 reply; 4+ messages in thread
From: Greg KH @ 2020-09-07 8:21 UTC (permalink / raw)
To: Christoph Hellwig; +Cc: arnd, linux-kernel, Christophe Leroy
On Mon, Sep 07, 2020 at 09:51:43AM +0200, Christoph Hellwig wrote:
> Christophe reported a major speedup due to avoiding the iov_iter
> overhead, so just add this trivial function.
>
> Suggested-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> Tested-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> ---
>
> Changes since v1:
> - fix the Suggested-by: tag
> - report the actually read bytes in case of a partial clear_user
> - remove an impossible to hit conditional
>
> drivers/char/mem.c | 28 ++++++++++++++++++++++++++++
> 1 file changed, 28 insertions(+)
I already merged your v1 into my tree, do you want me to revert that and
then add this, or can you send me the diff to apply instead? I can't
rebase my public trees.
thanks,
greg k-h
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH v2] /dev/zero: also implement ->read
2020-09-07 8:21 ` Greg KH
@ 2020-09-07 8:21 ` Christoph Hellwig
2020-09-07 8:45 ` Greg KH
0 siblings, 1 reply; 4+ messages in thread
From: Christoph Hellwig @ 2020-09-07 8:21 UTC (permalink / raw)
To: Greg KH; +Cc: Christoph Hellwig, arnd, linux-kernel, Christophe Leroy
On Mon, Sep 07, 2020 at 10:21:14AM +0200, Greg KH wrote:
> On Mon, Sep 07, 2020 at 09:51:43AM +0200, Christoph Hellwig wrote:
> > Christophe reported a major speedup due to avoiding the iov_iter
> > overhead, so just add this trivial function.
> >
> > Suggested-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> > Signed-off-by: Christoph Hellwig <hch@lst.de>
> > Tested-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> > ---
> >
> > Changes since v1:
> > - fix the Suggested-by: tag
> > - report the actually read bytes in case of a partial clear_user
> > - remove an impossible to hit conditional
> >
> > drivers/char/mem.c | 28 ++++++++++++++++++++++++++++
> > 1 file changed, 28 insertions(+)
>
> I already merged your v1 into my tree, do you want me to revert that and
> then add this, or can you send me the diff to apply instead? I can't
> rebase my public trees.
Sure, I can send an incremental one. I vaguely remembered you as one
of the quilt holdouts.
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH v2] /dev/zero: also implement ->read
2020-09-07 8:21 ` Christoph Hellwig
@ 2020-09-07 8:45 ` Greg KH
0 siblings, 0 replies; 4+ messages in thread
From: Greg KH @ 2020-09-07 8:45 UTC (permalink / raw)
To: Christoph Hellwig; +Cc: arnd, linux-kernel, Christophe Leroy
On Mon, Sep 07, 2020 at 10:21:39AM +0200, Christoph Hellwig wrote:
> On Mon, Sep 07, 2020 at 10:21:14AM +0200, Greg KH wrote:
> > On Mon, Sep 07, 2020 at 09:51:43AM +0200, Christoph Hellwig wrote:
> > > Christophe reported a major speedup due to avoiding the iov_iter
> > > overhead, so just add this trivial function.
> > >
> > > Suggested-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> > > Signed-off-by: Christoph Hellwig <hch@lst.de>
> > > Tested-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> > > ---
> > >
> > > Changes since v1:
> > > - fix the Suggested-by: tag
> > > - report the actually read bytes in case of a partial clear_user
> > > - remove an impossible to hit conditional
> > >
> > > drivers/char/mem.c | 28 ++++++++++++++++++++++++++++
> > > 1 file changed, 28 insertions(+)
> >
> > I already merged your v1 into my tree, do you want me to revert that and
> > then add this, or can you send me the diff to apply instead? I can't
> > rebase my public trees.
>
> Sure, I can send an incremental one. I vaguely remembered you as one
> of the quilt holdouts.
That's only for stable tree work :)
thanks for the incremental patch, will go apply that now.
greg k-h
^ permalink raw reply [flat|nested] 4+ messages in thread
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2020-09-07 7:51 [PATCH v2] /dev/zero: also implement ->read Christoph Hellwig
2020-09-07 8:21 ` Greg KH
2020-09-07 8:21 ` Christoph Hellwig
2020-09-07 8:45 ` Greg KH
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