Some embedded systems with tightly controlled userspace have no use
for /dev/zero, and could benefit from the size savings gained by
omitting it. Add a new EMBEDDED config option to disable it.
bloat-o-meter (based on tinyconfig):
add/remove: 0/3 grow/shrink: 0/1 up/down: 0/-391 (-391)
function old new delta
chr_dev_init 162 147 -15
mmap_zero 16 - -16
zero_fops 116 - -116
zero_bdi 244 - -244
Signed-off-by: Tom Zanussi <tom.zanu...@linux.intel.com>
---
drivers/char/Kconfig | 10 ++++++++++
drivers/char/mem.c | 15 +++++++++++----
2 files changed, 21 insertions(+), 4 deletions(-)
diff --git a/drivers/char/Kconfig b/drivers/char/Kconfig
index 17f6ddf..00f9b8a 100644
--- a/drivers/char/Kconfig
+++ b/drivers/char/Kconfig
@@ -46,6 +46,16 @@ config DEVNULL
systems with strictly controlled userspace may not need it.
When in doubt, say "Y".
+config DEVZERO
+ bool "/dev/zero virtual device support" if EMBEDDED
+ depends on DEVMEM_BASE
+ default y
+ help
+ Say Y here if you want to support the /dev/zero device. The
+ /dev/zero 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 25d6f5b..96f7a9d 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -633,7 +633,8 @@ static ssize_t __maybe_unused aio_write_null(struct kiocb
*iocb,
return iov_length(iov, nr_segs);
}
-static ssize_t read_iter_zero(struct kiocb *iocb, struct iov_iter *iter)
+static ssize_t __maybe_unused read_iter_zero(struct kiocb *iocb,
+ struct iov_iter *iter)
{
size_t written = 0;
@@ -652,6 +653,7 @@ static ssize_t read_iter_zero(struct kiocb *iocb, struct
iov_iter *iter)
return written;
}
+#ifdef CONFIG_DEVZERO
static int mmap_zero(struct file *file, struct vm_area_struct *vma)
{
#ifndef CONFIG_MMU
@@ -661,6 +663,7 @@ static int mmap_zero(struct file *file, struct
vm_area_struct *vma)
return shmem_zero_setup(vma);
return 0;
}
+#endif
static ssize_t write_full(struct file *file, const char __user *buf,
size_t count, loff_t *ppos)
@@ -767,6 +770,7 @@ static const struct file_operations port_fops = {
};
#endif
+#ifdef CONFIG_DEVZERO
static const struct file_operations zero_fops = {
.llseek = zero_lseek,
.read = new_sync_read,
@@ -785,6 +789,7 @@ static struct backing_dev_info zero_bdi = {
.name = "char/mem",
.capabilities = BDI_CAP_MAP_COPY | BDI_CAP_NO_ACCT_AND_WRITEBACK,
};
+#endif
static const struct file_operations full_fops = {
.llseek = full_lseek,
@@ -811,7 +816,9 @@ static const struct memdev {
#ifdef CONFIG_DEVPORT
[4] = { "port", 0, &port_fops, NULL },
#endif
+#ifdef CONFIG_DEVZERO
[5] = { "zero", 0666, &zero_fops, &zero_bdi },
+#endif
[7] = { "full", 0666, &full_fops, NULL },
[8] = { "random", 0666, &random_fops, NULL },
[9] = { "urandom", 0666, &urandom_fops, NULL },
@@ -864,12 +871,12 @@ static struct class *mem_class;
static int __init chr_dev_init(void)
{
int minor;
- int err;
- err = bdi_init(&zero_bdi);
+#ifdef CONFIG_DEVZERO
+ int err = bdi_init(&zero_bdi);
if (err)
return err;
-
+#endif
if (register_chrdev(MEM_MAJOR, "mem", &memory_fops))
printk("unable to get major %d for memory devs\n", MEM_MAJOR);
--
1.9.3
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
