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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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