[ARM] 4736/1: Export atags to userspace and allow kexec to use customised atags

Currently, the atags used by kexec are fixed to the ones originally used
to boot the kernel. This is less than ideal as changing the commandline,
initrd and other options would be a useful feature.

This patch exports the atags used for the current kernel to userspace
through an "atags" file in procfs. The presence of the file is
controlled by its own Kconfig option and cleans up several ifdef blocks
into a separate file. The tags for the new kernel are assumed to be at
a fixed location before the kernel image itself. The location of the
tags used to boot the original kernel is unimportant and no longer
saved.

Based on a patch from Uli Luckas <u.luckas@road.de>

Signed-off-by: Richard Purdie <rpurdie@rpsys.net>
Acked-by: Uli Luckas <u.luckas@road.de>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 86 insertions, 0 deletions

diff --git a/arch/arm/kernel/atags.c b/arch/arm/kernel/atags.c
new file mode 100644
index 00000000000..e2e934c3808
--- /dev/null
+++ b/arch/arm/kernel/atags.c
@@ -0,0 +1,86 @@
+#include <linux/slab.h>
+#include <linux/kexec.h>
+#include <linux/proc_fs.h>
+#include <asm/setup.h>
+#include <asm/types.h>
+#include <asm/page.h>
+
+struct buffer {
+	size_t size;
+	char *data;
+};
+static struct buffer tags_buffer;
+
+static int
+read_buffer(char* page, char** start, off_t off, int count,
+	int* eof, void* data)
+{
+	struct buffer *buffer = (struct buffer *)data;
+
+	if (off >= buffer->size) {
+		*eof = 1;
+		return 0;
+	}
+
+	count = min((int) (buffer->size - off), count);
+
+	memcpy(page, &buffer->data[off], count);
+
+	return count;
+}
+
+
+static int
+create_proc_entries(void)
+{
+	struct proc_dir_entry* tags_entry;
+
+	tags_entry = create_proc_read_entry("atags", 0400, &proc_root, read_buffer, &tags_buffer);
+	if (!tags_entry)
+		return -ENOMEM;
+
+	return 0;
+}
+
+
+static char __initdata atags_copy_buf[KEXEC_BOOT_PARAMS_SIZE];
+static char __initdata *atags_copy;
+
+void __init save_atags(const struct tag *tags)
+{
+	atags_copy = atags_copy_buf;
+	memcpy(atags_copy, tags, KEXEC_BOOT_PARAMS_SIZE);
+}
+
+
+static int __init init_atags_procfs(void)
+{
+	struct tag *tag;
+	int error;
+
+	if (!atags_copy) {
+		printk(KERN_WARNING "Exporting ATAGs: No saved tags found\n");
+		return -EIO;
+	}
+
+	for (tag = (struct tag *) atags_copy; tag->hdr.size; tag = tag_next(tag))
+		;
+
+	tags_buffer.size = ((char *) tag - atags_copy) + sizeof(tag->hdr);
+	tags_buffer.data = kmalloc(tags_buffer.size, GFP_KERNEL);
+	if (tags_buffer.data == NULL)
+		return -ENOMEM;
+	memcpy(tags_buffer.data, atags_copy, tags_buffer.size);
+
+	error = create_proc_entries();
+	if (error) {
+		printk(KERN_ERR "Exporting ATAGs: not enough memory\n");
+		kfree(tags_buffer.data);
+		tags_buffer.size = 0;
+		tags_buffer.data = NULL;
+	}
+
+	return error;
+}
+
+arch_initcall(init_atags_procfs);