drivers/char/mem: implement splice() for /dev/zero, /dev/full
Commit Message
This allows splicing zeroed pages into a pipe, and allows discarding
pages from a pipe by splicing them to /dev/zero. Writing to /dev/zero
should have the same effect as writing to /dev/null, and a
"splice_write" implementation exists only for /dev/null.
(The /dev/zero splice_read implementation could be optimized by
pushing references to the global zero page to the pipe, but that's an
optimization for another day.)
Signed-off-by: Max Kellermann <max.kellermann@ionos.com>
---
drivers/char/mem.c | 4 ++++
1 file changed, 4 insertions(+)
@@ -640,6 +640,7 @@ static int open_port(struct inode *inode, struct file *filp)
#define full_lseek null_lseek
#define write_zero write_null
#define write_iter_zero write_iter_null
+#define splice_write_zero splice_write_null
#define open_mem open_port
static const struct file_operations __maybe_unused mem_fops = {
@@ -677,6 +678,8 @@ static const struct file_operations zero_fops = {
.read_iter = read_iter_zero,
.read = read_zero,
.write_iter = write_iter_zero,
+ .splice_read = copy_splice_read,
+ .splice_write = splice_write_zero,
.mmap = mmap_zero,
.get_unmapped_area = get_unmapped_area_zero,
#ifndef CONFIG_MMU
@@ -688,6 +691,7 @@ static const struct file_operations full_fops = {
.llseek = full_lseek,
.read_iter = read_iter_zero,
.write = write_full,
+ .splice_read = copy_splice_read,
};
static const struct memdev {