Messages in this thread | | | Subject | Re: [PATCH] /dev/zero: also implement ->read | From | Christophe Leroy <> | Date | Thu, 3 Sep 2020 19:51:07 +0200 |
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Le 03/09/2020 à 17:59, Christoph Hellwig a écrit : > Christophe reported a major speedup due to avoiding the iov_iter > overhead, so just add this trivial function. Note that /dev/zero > already implements both an iter and non-iter writes so this just > makes it more symmetric. > > Christophe Leroy <christophe.leroy@csgroup.eu> > Signed-off-by: Christoph Hellwig <hch@lst.de> > --- > drivers/char/mem.c | 22 ++++++++++++++++++++++ > 1 file changed, 22 insertions(+) > > diff --git a/drivers/char/mem.c b/drivers/char/mem.c > index abd4ffdc8cdebc..1dc99ab158457a 100644 > --- a/drivers/char/mem.c > +++ b/drivers/char/mem.c > @@ -726,6 +726,27 @@ 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); > + > + if (clear_user(buf + cleared, chunk)) > + return cleared ? cleared : -EFAULT; > + cleared += chunk; > + count -= chunk; > + > + if (signal_pending(current)) > + return cleared ? cleared : -ERESTARTSYS; > + cond_resched(); > + } > + > + return cleared; > +} > + > static int mmap_zero(struct file *file, struct vm_area_struct *vma) > { > #ifndef CONFIG_MMU > @@ -921,6 +942,7 @@ static const struct file_operations zero_fops = { > .llseek = zero_lseek, > .write = write_zero, > .read_iter = read_iter_zero, > + .read = read_zero,
Wondering if .read should be before .write, so that we get in order read, write, read_iter, write_iter.
> .write_iter = write_iter_zero, > .mmap = mmap_zero, > .get_unmapped_area = get_unmapped_area_zero, >
Christophe
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