Some embedded systems with tightly controlled userspace have no use
for /dev/null, and could benefit from the size savings gained by
omitting it. Add a new EMBEDDED config option to disable it.
write_null() and aio_write_null() are shared between /dev/null and
/dev/zero; making it __maybe_unused prevents them from emitting
warnings if both devices are compiled out, while avoiding ugly
compound ifdefs. Similarly for null_lseek, shared between /dev/null,
/dev/zero, and /dev/full.
bloat-o-meter (based on tinyconfig):
add/remove: 0/5 grow/shrink: 0/0 up/down: 0/-150 (-150)
function old new delta
read_null 3 - -3
aio_read_null 3 - -3
pipe_to_null 4 - -4
splice_write_null 24 - -24
null_fops 116 - -116
bloat-o-meter showing the difference between only CONFIG_DEVZERO and
CONFIG_DEVFULL off and both those plus CONFIG_DEVNULL off:
add/remove: 0/8 grow/shrink: 0/0 up/down: 0/-196 (-196)
function old new delta
write_null 3 - -3
read_null 3 - -3
aio_read_null 3 - -3
pipe_to_null 4 - -4
aio_write_null 18 - -18
splice_write_null 24 - -24
null_lseek 25 - -25
null_fops 116 - -116
So with DEVZERO also configured out, we see the shared write_null,
aio_write_null, and null_lseek drop out.
Signed-off-by: Tom Zanussi <tom.zanu...@linux.intel.com>
---
drivers/char/Kconfig | 10 ++++++++++
drivers/char/mem.c | 35 ++++++++++++++++++++++-------------
2 files changed, 32 insertions(+), 13 deletions(-)
diff --git a/drivers/char/Kconfig b/drivers/char/Kconfig
index 5a6c060..17f6ddf 100644
--- a/drivers/char/Kconfig
+++ b/drivers/char/Kconfig
@@ -36,6 +36,16 @@ config DEVMEM
disabled on systems that will never use either, such as many
embedded systems. When in doubt, say "Y".
+config DEVNULL
+ bool "/dev/null virtual device support" if EMBEDDED
+ depends on DEVMEM_BASE
+ default y
+ help
+ Say Y here if you want to support the /dev/null device. The
+ /dev/null device is used by many programs, but some embedded
+ systems with strictly controlled userspace may not need it.
+ When in doubt, say "Y".
+
config SGI_SNSC
bool "SGI Altix system controller communication support"
depends on (IA64_SGI_SN2 || IA64_GENERIC)
diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index 5944d87..25d6f5b 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -593,30 +593,19 @@ static ssize_t write_port(struct file *file, const char
__user *buf,
}
#endif
+#ifdef CONFIG_DEVNULL
static ssize_t read_null(struct file *file, char __user *buf,
size_t count, loff_t *ppos)
{
return 0;
}
-static ssize_t write_null(struct file *file, const char __user *buf,
- size_t count, loff_t *ppos)
-{
- return count;
-}
-
static ssize_t aio_read_null(struct kiocb *iocb, const struct iovec *iov,
unsigned long nr_segs, loff_t pos)
{
return 0;
}
-static ssize_t aio_write_null(struct kiocb *iocb, const struct iovec *iov,
- unsigned long nr_segs, loff_t pos)
-{
- return iov_length(iov, nr_segs);
-}
-
static int pipe_to_null(struct pipe_inode_info *info, struct pipe_buffer *buf,
struct splice_desc *sd)
{
@@ -628,6 +617,21 @@ static ssize_t splice_write_null(struct pipe_inode_info
*pipe, struct file *out,
{
return splice_from_pipe(pipe, out, ppos, len, flags, pipe_to_null);
}
+#endif
+
+static ssize_t __maybe_unused write_null(struct file *file,
+ const char __user *buf,
+ size_t count, loff_t *ppos)
+{
+ return count;
+}
+
+static ssize_t __maybe_unused aio_write_null(struct kiocb *iocb,
+ const struct iovec *iov,
+ unsigned long nr_segs, loff_t pos)
+{
+ return iov_length(iov, nr_segs);
+}
static ssize_t read_iter_zero(struct kiocb *iocb, struct iov_iter *iter)
{
@@ -669,7 +673,8 @@ static ssize_t write_full(struct file *file, const char
__user *buf,
* can fopen() both devices with "a" now. This was previously impossible.
* -- SRB.
*/
-static loff_t null_lseek(struct file *file, loff_t offset, int orig)
+static loff_t __maybe_unused null_lseek(struct file *file, loff_t offset,
+ int orig)
{
return file->f_pos = 0;
}
@@ -742,6 +747,7 @@ static const struct file_operations kmem_fops = {
};
#endif
+#ifdef CONFIG_DEVNULL
static const struct file_operations null_fops = {
.llseek = null_lseek,
.read = read_null,
@@ -750,6 +756,7 @@ static const struct file_operations null_fops = {
.aio_write = aio_write_null,
.splice_write = splice_write_null,
};
+#endif
#ifdef CONFIG_DEVPORT
static const struct file_operations port_fops = {
@@ -798,7 +805,9 @@ static const struct memdev {
#ifdef CONFIG_DEVKMEM
[2] = { "kmem", 0, &kmem_fops, &directly_mappable_cdev_bdi },
#endif
+#ifdef CONFIG_DEVNULL
[3] = { "null", 0666, &null_fops, NULL },
+#endif
#ifdef CONFIG_DEVPORT
[4] = { "port", 0, &port_fops, NULL },
#endif
--
1.9.3
--
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