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drivers/char/mem: implement splice() for /dev/zero, /dev/full 

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>
Link: https://lore.kernel.org/r/20230919073743.1066313-1-max.kellermann@ionos.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Max Kellermann 2023-09-19 09:37:42 +02:00 committed by Greg Kroah-Hartman
parent 19e3e6cdfd
commit 1b057bd800
1 changed files with 4 additions and 0 deletions
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4
drivers/char/mem.c
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@ -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 {