dma-debug: add debugfs file for driver filter

This patch adds the dma-api/driver_filter file to debugfs. The root user
can write a driver name into this file to see only dma-api errors for
that particular driver in the kernel log. Writing an empty string to
that file disables the driver filter.

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>

1 files changed, 101 insertions, 1 deletions

diff --git a/lib/dma-debug.c b/lib/dma-debug.c
index c01f64780caf..c6330b1a7be7 100644
--- a/lib/dma-debug.c
+++ b/lib/dma-debug.c
@@ -23,9 +23,11 @@
 #include <linux/dma-debug.h>
 #include <linux/spinlock.h>
 #include <linux/debugfs.h>
+#include <linux/uaccess.h>
 #include <linux/device.h>
 #include <linux/types.h>
 #include <linux/sched.h>
+#include <linux/ctype.h>
 #include <linux/list.h>
 #include <linux/slab.h>
 
@@ -98,6 +100,7 @@ static struct dentry *show_all_errors_dent  __read_mostly;
 static struct dentry *show_num_errors_dent  __read_mostly;
 static struct dentry *num_free_entries_dent __read_mostly;
 static struct dentry *min_free_entries_dent __read_mostly;
+static struct dentry *filter_dent           __read_mostly;
 
 /* per-driver filter related state */
 
@@ -160,7 +163,8 @@ static bool driver_filter(struct device *dev)
                 read_lock_irqsave(&driver_name_lock, flags);
 
                 if (drv->name &&
-                    strncmp(current_driver_name, drv->name, 63) == 0) {
+                    strncmp(current_driver_name, drv->name,
+                            NAME_MAX_LEN-1) == 0) {
                         current_driver = drv;
                         ret = true;
                 }
@@ -454,6 +458,97 @@ out_err:
         return -ENOMEM;
 }
 
+static ssize_t filter_read(struct file *file, char __user *user_buf,
+                           size_t count, loff_t *ppos)
+{
+        unsigned long flags;
+        char buf[NAME_MAX_LEN + 1];
+        int len;
+
+        if (!current_driver_name[0])
+                return 0;
+
+        /*
+         * We can't copy to userspace directly because current_driver_name can
+         * only be read under the driver_name_lock with irqs disabled. So
+         * create a temporary copy first.
+         */
+        read_lock_irqsave(&driver_name_lock, flags);
+        len = scnprintf(buf, NAME_MAX_LEN + 1, "%s\n", current_driver_name);
+        read_unlock_irqrestore(&driver_name_lock, flags);
+
+        return simple_read_from_buffer(user_buf, count, ppos, buf, len);
+}
+
+static ssize_t filter_write(struct file *file, const char __user *userbuf,
+                            size_t count, loff_t *ppos)
+{
+        unsigned long flags;
+        char buf[NAME_MAX_LEN];
+        size_t len = NAME_MAX_LEN - 1;
+        int i;
+
+        /*
+         * We can't copy from userspace directly. Access to
+         * current_driver_name is protected with a write_lock with irqs
+         * disabled. Since copy_from_user can fault and may sleep we
+         * need to copy to temporary buffer first
+         */
+        len = min(count, len);
+        if (copy_from_user(buf, userbuf, len))
+                return -EFAULT;
+
+        buf[len] = 0;
+
+        write_lock_irqsave(&driver_name_lock, flags);
+
+        /* Now handle the string we got from userspace very carefully.
+         * The rules are:
+         *         - only use the first token we got
+         *         - token delimiter is everything looking like a space
+         *           character (' ', '\n', '\t' ...)
+         *
+         */
+        if (!isalnum(buf[0])) {
+                /*
+                   If the first character userspace gave us is not
+                 * alphanumerical then assume the filter should be
+                 * switched off.
+                 */
+                if (current_driver_name[0])
+                        printk(KERN_INFO "DMA-API: switching off dma-debug "
+                                         "driver filter\n");
+                current_driver_name[0] = 0;
+                current_driver = NULL;
+                goto out_unlock;
+        }
+
+        /*
+         * Now parse out the first token and use it as the name for the
+         * driver to filter for.
+         */
+        for (i = 0; i < NAME_MAX_LEN; ++i) {
+                current_driver_name[i] = buf[i];
+                if (isspace(buf[i]) || buf[i] == ' ' || buf[i] == 0)
+                        break;
+        }
+        current_driver_name[i] = 0;
+        current_driver = NULL;
+
+        printk(KERN_INFO "DMA-API: enable driver filter for driver [%s]\n",
+               current_driver_name);
+
+out_unlock:
+        write_unlock_irqrestore(&driver_name_lock, flags);
+
+        return count;
+}
+
+const struct file_operations filter_fops = {
+        .read  = filter_read,
+        .write = filter_write,
+};
+
 static int dma_debug_fs_init(void)
 {
         dma_debug_dent = debugfs_create_dir("dma-api", NULL);
@@ -497,6 +592,11 @@ static int dma_debug_fs_init(void)
         if (!min_free_entries_dent)
                 goto out_err;
 
+        filter_dent = debugfs_create_file("driver_filter", 0644,
+                                          dma_debug_dent, NULL, &filter_fops);
+        if (!filter_dent)
+                goto out_err;
+
         return 0;
 
 out_err: