From 99f667352f6c938440d9043d0f66f859d6f3d50d Mon Sep 17 00:00:00 2001 From: Christoph Hellwig Date: Thu, 3 Sep 2020 17:59:22 +0200 Subject: [PATCH] /dev/zero: also implement ->read 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. Tested-by: Christophe Leroy Signed-off-by: Christoph Hellwig Link: https://lore.kernel.org/r/20200903155922.1111551-1-hch@lst.de Signed-off-by: Greg Kroah-Hartman --- drivers/char/mem.c | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) diff --git a/drivers/char/mem.c b/drivers/char/mem.c index abd4ffdc8cde..1dc99ab15845 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, .write_iter = write_iter_zero, .mmap = mmap_zero, .get_unmapped_area = get_unmapped_area_zero,