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Subject[PATCH v3 3/3] char drivers: ramoops debugfs entry
Date
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.

The entry added is /sys/kernel/debug/ramoops/next

The entry returns a dump of size record_size each time, skipping invalid
dumps. When it reaches the end of the memory area reserved for dumps it
returns an empty record and resets the current record count.

Change-Id: Ifbab9af833be9ee0bc1c33bc9871f2fc0eb9d228
Signed-off-by: Sergiu Iordache <sergiu@chromium.org>
---
drivers/char/ramoops.c | 113 +++++++++++++++++++++++++++++++++++++++++++++++-
1 files changed, 111 insertions(+), 2 deletions(-)
diff --git a/drivers/char/ramoops.c b/drivers/char/ramoops.c
index bd9b94b..791084c 100644
--- a/drivers/char/ramoops.c
+++ b/drivers/char/ramoops.c
@@ -30,9 +30,13 @@
#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_NEXT "next"

static ulong record_size = MIN_MEM_SIZE;
module_param(record_size, ulong, 0400);
@@ -61,12 +65,81 @@ static struct ramoops_context {
unsigned long size;
unsigned long record_size;
int dump_oops;
+ int current_entry;
int count;
int max_count;
} oops_cxt;

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_next_entry;
+
+/*
+ * Entry to have access to the memory logged by ramoops. The way the data
+ * is returned is as follows:
+ * Data records are checked one by one for the existence of the header.
+ * If a valid record is found data is returned from it, otherwise it is
+ * skipped.
+ * Once all the records are checked the next call after the last record
+ * will return an empty buffer and the counter is reset.
+ */
+static ssize_t ramoops_read_next(struct file *file, char __user *buf,
+ size_t count, loff_t *ppos)
+{
+ struct ramoops_context *cxt = &oops_cxt;
+
+ mutex_lock(&ramoops_mutex);
+
+ /* Do this check here so it returns an empty file once it resets */
+ if (cxt->current_entry >= cxt->max_count) {
+ cxt->current_entry = 0;
+ count = 0;
+ goto out;
+ }
+
+ /* Check to see if the current dump is valid */
+ while (cxt->current_entry < cxt->max_count
+ && memcmp(cxt->virt_addr + cxt->record_size *
+ cxt->current_entry, RAMOOPS_KERNMSG_HDR,
+ strlen(RAMOOPS_KERNMSG_HDR)))
+ cxt->current_entry++;
+
+ /* In case a dump was not found return 0 */
+ if (cxt->current_entry >= cxt->max_count) {
+ count = 0;
+ goto out;
+ }
+
+ /* Otherwise proceed as normal to return the data */
+ if (*ppos + count > cxt->record_size)
+ count = cxt->record_size - *ppos;
+ if (*ppos > cxt->record_size) {
+ count = 0;
+ cxt->current_entry++;
+ goto out;
+ }
+ if (copy_to_user(buf, cxt->virt_addr + cxt->record_size *
+ cxt->current_entry + *ppos, count)) {
+ count = -EFAULT;
+ goto out;
+ }
+ *ppos += count;
+
+ /* completed reading this part, go to the next one */
+ if (*ppos == cxt->record_size)
+ cxt->current_entry++;
+
+out:
+ mutex_unlock(&ramoops_mutex);
+ return count;
+}
+
+static const struct file_operations ramoops_next_fops = {
+ .read = ramoops_read_next,
+};

static void ramoops_do_dump(struct kmsg_dumper *dumper,
enum kmsg_dump_reason reason, const char *s1, unsigned long l1,
@@ -89,6 +162,7 @@ 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 +184,7 @@ 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)
@@ -128,8 +203,8 @@ static int __init ramoops_probe(struct platform_device *pdev)
rounddown_pow_of_two(pdata->record_size);

/* Check for the minimum memory size */
- if (pdata->mem_size < MIN_MEM_SIZE &&
- pdata->record_size < MIN_MEM_SIZE) {
+ if (pdata->mem_size < MIN_MEM_SIZE
+ && pdata->record_size < MIN_MEM_SIZE) {
pr_err("memory size too small, minium is %lu\n", MIN_MEM_SIZE);
goto fail3;
}
@@ -145,6 +220,7 @@ static int __init ramoops_probe(struct platform_device *pdev)
cxt->size = pdata->mem_size;
cxt->phys_addr = pdata->mem_address;
cxt->record_size = pdata->record_size;
+ cxt->current_entry = 0;
cxt->dump_oops = pdata->dump_oops;

if (!request_mem_region(cxt->phys_addr, cxt->size, "ramoops")) {
@@ -166,6 +242,30 @@ 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;
+ }
+
+ /*
+ * This interface exposes the next valid entry from ramoops, starting
+ * from the start of memory area. Once there are no more entries it
+ * returns an empty buffer. Reading the entry again afterwards starts
+ * from the begining.
+ */
+ ramoops_next_entry = debugfs_create_file(RAMOOPS_NEXT, 0444,
+ ramoops_dir, NULL, &ramoops_next_fops);
+
+ if (ramoops_next_entry == NULL) {
+ err = -ENOMEM;
+ pr_err("debugfs next entry creation failed\n");
+ goto no_ramoops_next;
+ }
+
+
return 0;

fail1:
@@ -174,6 +274,11 @@ fail2:
release_mem_region(cxt->phys_addr, cxt->size);
fail3:
return err;
+
+no_ramoops_next:
+ debugfs_remove(ramoops_dir);
+out:
+ return err;
}

static int __exit ramoops_remove(struct platform_device *pdev)
@@ -231,6 +336,10 @@ static void __exit ramoops_exit(void)
{
platform_driver_unregister(&ramoops_driver);
kfree(dummy_data);
+
+ /* Clean up debugfs entries */
+ debugfs_remove(ramoops_next_entry);
+ debugfs_remove(ramoops_dir);
}

module_init(ramoops_init);
--
1.7.3.1


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