[PATCH v2 3/3] char drivers: ramoops debugfs entry

[Sergiu Iordache <sergiu@chromium.org>]

While ramoops writes to ram, accessing the dump requires using /dev/mem
and knowing the memory location (or a similar solution). This patch
provides a debugfs interface through which the respective memory
area can be easily accessed. It also adds an entry to expose the record
size which must be used to divide the memory area into individual dumps
and a dump count entry.

The entries added are:
/sys/kernel/debug/ramoops/full - memory dump of the whole reserved area.
/sys/kernel/debug/ramoops/count - number of dumps currently present
(will be 0 after a restart).

Change-Id: Ifbab9af833be9ee0bc1c33bc9871f2fc0eb9d228
Signed-off-by: Sergiu Iordache <sergiu@chromium.org>
---
The patch was built on the 2.6.38 kernel and is based on the following
patches which were applied from the mmotm tree:
ramoops-add-new-line-to-each-print
ramoops-use-module-parameters-instead-of-platform-data-if-not-available
ramoops-use-module-parameters-instead-of-platform-data-if-not-available-checkpatch-fixes

 drivers/char/ramoops.c |  101 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 101 insertions(+), 0 deletions(-)

diff --git a/drivers/char/ramoops.c b/drivers/char/ramoops.c
index f34077e..9c0e30e 100644
--- a/drivers/char/ramoops.c
+++ b/drivers/char/ramoops.c
@@ -30,9 +30,15 @@
 #include <linux/platform_device.h>
 #include <linux/slab.h>
 #include <linux/ramoops.h>
+#include <linux/uaccess.h>
+#include <linux/debugfs.h>
 
 #define RAMOOPS_KERNMSG_HDR "===="
 #define MIN_MEM_SIZE 4096UL
+#define RAMOOPS_DIR "ramoops"
+#define RAMOOPS_FULL "full"
+#define RAMOOPS_RS "record_size"
+#define RAMOOPS_COUNT "count"
 
 static ulong record_size = 4096UL;
 module_param(record_size, ulong, 0400);
@@ -67,6 +73,39 @@ static struct ramoops_context {
 
 static struct platform_device *dummy;
 static struct ramoops_platform_data *dummy_data;
+static DEFINE_MUTEX(ramoops_mutex);
+
+/* Debugfs entries for ramoops */
+static struct dentry *ramoops_dir, *ramoops_full_entry, *ramoops_rs_entry,
+				*ramoops_count_entry;
+
+/* Entry to have access to the whole memory area */
+static ssize_t ramoops_read_full(struct file *file, char __user *buf,
+					size_t count, loff_t *ppos)
+{
+	struct ramoops_context *cxt = &oops_cxt;
+
+	mutex_lock(&ramoops_mutex);
+	if (*ppos + count > cxt->size)
+		count = cxt->size - *ppos;
+	if (*ppos > cxt->size) {
+		count = 0;
+		goto out;
+	}
+	if (copy_to_user(buf, cxt->virt_addr + *ppos, count)) {
+		count = -EFAULT;
+		goto out;
+	}
+	*ppos += count;
+
+out:
+	mutex_unlock(&ramoops_mutex);
+	return count;
+}
+
+static const struct file_operations ramoops_full_fops = {
+	.read = ramoops_read_full,
+};
 
 static void ramoops_do_dump(struct kmsg_dumper *dumper,
 		enum kmsg_dump_reason reason, const char *s1, unsigned long l1,
@@ -89,6 +128,7 @@ static void ramoops_do_dump(struct kmsg_dumper *dumper,
 	if (reason == KMSG_DUMP_OOPS && !cxt->dump_oops)
 		return;
 
+	mutex_lock(&ramoops_mutex);
 	buf = cxt->virt_addr + (cxt->count * cxt->record_size);
 	buf_orig = buf;
 
@@ -110,6 +150,7 @@ static void ramoops_do_dump(struct kmsg_dumper *dumper,
 	memcpy(buf + l1_cpy, s2 + s2_start, l2_cpy);
 
 	cxt->count = (cxt->count + 1) % cxt->max_count;
+	mutex_unlock(&ramoops_mutex);
 }
 
 static int __init ramoops_probe(struct platform_device *pdev)
@@ -168,6 +209,51 @@ static int __init ramoops_probe(struct platform_device *pdev)
 		goto fail1;
 	}
 
+	/* Initialize debugfs entry so the memory can be easily accessed */
+	ramoops_dir = debugfs_create_dir(RAMOOPS_DIR, NULL);
+	if (ramoops_dir == NULL) {
+		err = -ENOMEM;
+		pr_err("debugfs directory entry creation failed\n");
+		goto out;
+	}
+
+	ramoops_full_entry = debugfs_create_file(RAMOOPS_FULL, 0444,
+					ramoops_dir, NULL, &ramoops_full_fops);
+
+	if (ramoops_full_entry == NULL) {
+		err = -ENOMEM;
+		pr_err("debugfs full entry creation failed\n");
+		goto no_ramoops_full;
+	}
+
+	/*
+	 * Since ramoops returns records of record_size it is useful to
+	 * know the record size from userspace so we can parse the result
+	 * Since the record size is usually small we don't mind converting
+	 * it to a u32 from ulong.
+	 */
+	ramoops_rs_entry = debugfs_create_u32(RAMOOPS_RS, 0444,
+					ramoops_dir, (u32 *)&cxt->record_size);
+
+	if (ramoops_rs_entry == NULL) {
+		err = -ENOMEM;
+		pr_err("debugfs record size entry creation failed\n");
+		goto no_ramoops_rs;
+	}
+
+	ramoops_count_entry = debugfs_create_u32(RAMOOPS_COUNT, 0444,
+					ramoops_dir, (u32 *)&cxt->count);
+
+	/*
+	 * Also add a count entry in debugfs. However this count is reset
+	 * in case the machine resets so it is not always useful.
+	 */
+	if (ramoops_count_entry == NULL) {
+		err = -ENOMEM;
+		pr_err("debugfs record size entry creation failed\n");
+		goto no_ramoops_count;
+	}
+
 	return 0;
 
 fail1:
@@ -176,6 +262,15 @@ fail2:
 	release_mem_region(cxt->phys_addr, cxt->size);
 fail3:
 	return err;
+
+no_ramoops_count:
+	debugfs_remove(ramoops_rs_entry);
+no_ramoops_rs:
+	debugfs_remove(ramoops_full_entry);
+no_ramoops_full:
+	debugfs_remove(ramoops_dir);
+out:
+	return err;
 }
 
 static int __exit ramoops_remove(struct platform_device *pdev)
@@ -233,6 +328,12 @@ static void __exit ramoops_exit(void)
 {
 	platform_driver_unregister(&ramoops_driver);
 	kfree(dummy_data);
+
+	/* Clean up debugfs entries */
+	debugfs_remove(ramoops_full_entry);
+	debugfs_remove(ramoops_rs_entry);
+	debugfs_remove(ramoops_count_entry);
+	debugfs_remove(ramoops_dir);
 }
 
 module_init(ramoops_init);
-- 
1.7.3.1