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authorChristoph Hellwig <hch@lst.de>2020-09-03 17:59:22 +0200
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2020-09-03 19:50:47 +0200
commit99f667352f6c938440d9043d0f66f859d6f3d50d (patch)
treebf5c687509f17d774cd978ac684c2a2c157d6ca2 /drivers/char/mem.c
parent261e7818f06ec51e488e007f787ccd7e77272918 (diff)
/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 <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>
Diffstat (limited to 'drivers/char/mem.c')
-rw-r--r--drivers/char/mem.c22
1 files changed, 22 insertions, 0 deletions
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,