/dev/zero: also implement ->read (99f66735) · Commits · 戴 / test

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 <christophe.leroy@csgroup.eu> Signed-off-by:

Christoph Hellwig <hch@lst.de> Link: https://lore.kernel.org/r/20200903155922.1111551-1-hch@lst.de Signed-off-by:

Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/char/mem.c

+22 −0

Original line number	Diff line number	Diff line
		@@ -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,

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