UBI: allow direct user-space I/O

Introduce a new ioctl UBI_IOCSETPROP to set properties
on a volume. Also add the first property:
UBI_PROP_DIRECT_WRITE, this property is used to set the
ability to use direct writes in userspace

Signed-off-by: Sidney Amani <[e-mail]>
Signed-off-by: Corentin Chary <[e-mail]>
Signed-off-by: Artem Bityutskiy <[e-mail]>

drivers/mtd/ubi/Kconfig.debug

···
 	  This option switches the background thread off by default. The thread
 	  may be also be enabled/disabled via UBI sysfs.
 
-config MTD_UBI_DEBUG_USERSPACE_IO
-	bool "Direct user-space write/erase support"
-	default n
-	depends on MTD_UBI_DEBUG
-	help
-	  By default, users cannot directly write and erase individual
-	  eraseblocks of dynamic volumes, and have to use update operation
-	  instead. This option enables this capability - it is very useful for
-	  debugging and testing.
-
 config MTD_UBI_DEBUG_EMULATE_BITFLIPS
 	bool "Emulate flash bit-flips"
 	depends on MTD_UBI_DEBUG

drivers/mtd/ubi/cdev.c

···
 	return err ? err : count_save - count;
 }
 
-#ifdef CONFIG_MTD_UBI_DEBUG_USERSPACE_IO
-
 /*
  * This function allows to directly write to dynamic UBI volumes, without
- * issuing the volume update operation. Available only as a debugging feature.
- * Very useful for testing UBI.
+ * issuing the volume update operation.
  */
 static ssize_t vol_cdev_direct_write(struct file *file, const char __user *buf,
 				     size_t count, loff_t *offp)
···
 	int lnum, off, len, tbuf_size, err = 0;
 	size_t count_save = count;
 	char *tbuf;
+
+	if (!vol->direct_writes)
+		return -EPERM;
 
 	dbg_gen("requested: write %zd bytes to offset %lld of volume %u",
 		count, *offp, vol->vol_id);
···
 	vfree(tbuf);
 	return err ? err : count_save - count;
 }
-
-#else
-#define vol_cdev_direct_write(file, buf, count, offp) (-EPERM)
-#endif /* CONFIG_MTD_UBI_DEBUG_USERSPACE_IO */
 
 static ssize_t vol_cdev_write(struct file *file, const char __user *buf,
 			      size_t count, loff_t *offp)
···
 			break;
 		}
 		err = ubi_is_mapped(desc, lnum);
+		break;
+	}
+
+	/* Set volume property command*/
+	case UBI_IOCSETPROP:
+	{
+		struct ubi_set_prop_req req;
+
+		err = copy_from_user(&req, argp,
+				sizeof(struct ubi_set_prop_req));
+		if (err) {
+			err = -EFAULT;
+			break;
+		}
+		switch (req.property) {
+		case UBI_PROP_DIRECT_WRITE:
+			mutex_lock(&ubi->volumes_mutex);
+			desc->vol->direct_writes = !!req.value;
+			mutex_unlock(&ubi->volumes_mutex);
+			break;
+		default:
+			err = -EINVAL;
+			break;
+		}
 		break;
 	}
 

drivers/mtd/ubi/ubi.h

···
  * @upd_marker: %1 if the update marker is set for this volume
  * @updating: %1 if the volume is being updated
  * @changing_leb: %1 if the atomic LEB change ioctl command is in progress
+ * @direct_writes: %1 if direct writes are enabled for this volume
  *
  * @gluebi_desc: gluebi UBI volume descriptor
  * @gluebi_refcount: reference count of the gluebi MTD device
···
 	unsigned int upd_marker:1;
 	unsigned int updating:1;
 	unsigned int changing_leb:1;
+	unsigned int direct_writes:1;
 
 #ifdef CONFIG_MTD_UBI_GLUEBI
 	/*
···
  * @vtbl_size: size of the volume table in bytes
  * @vtbl: in-RAM volume table copy
  * @volumes_mutex: protects on-flash volume table and serializes volume
- *                 changes, like creation, deletion, update, re-size and re-name
+ *                 changes, like creation, deletion, update, re-size,
+ *                 re-name and set property
  *
  * @max_ec: current highest erase counter value
  * @mean_ec: current mean erase counter value

include/mtd/ubi-user.h

···
  * To check if a logical eraseblock is mapped to a physical eraseblock, the
  * %UBI_IOCEBISMAP ioctl command should be used. It returns %0 if the LEB is
  * not mapped, and %1 if it is mapped.
+ *
+ * Set an UBI volume property
+ * ~~~~~~~~~~~~~~~~~~~~~~~~~
+ *
+ * To set an UBI volume property the %UBI_IOCSETPROP ioctl command should be
+ * used. A pointer to a &struct ubi_set_prop_req object is expected to be
+ * passed. The object describes which property should be set, and to which value
+ * it should be set.
  */
 
 /*
···
 #define UBI_IOCEBUNMAP _IOW(UBI_VOL_IOC_MAGIC, 4, int32_t)
 /* Check if LEB is mapped command */
 #define UBI_IOCEBISMAP _IOR(UBI_VOL_IOC_MAGIC, 5, int32_t)
+/* Set an UBI volume property */
+#define UBI_IOCSETPROP _IOW(UBI_VOL_IOC_MAGIC, 6, struct ubi_set_prop_req)
 
 /* Maximum MTD device name length supported by UBI */
 #define MAX_UBI_MTD_NAME_LEN 127
···
 enum {
 	UBI_DYNAMIC_VOLUME = 3,
 	UBI_STATIC_VOLUME  = 4,
+};
+
+/*
+ * UBI set property ioctl constants
+ *
+ * @UBI_PROP_DIRECT_WRITE: allow / disallow user to directly write and
+ *                         erase individual eraseblocks on dynamic volumes
+ */
+enum {
+       UBI_PROP_DIRECT_WRITE = 1,
 };
 
 /**
···
 	int8_t  dtype;
 	int8_t  padding[3];
 } __attribute__ ((packed));
+
+
+/**
+ * struct ubi_set_prop_req - a data structure used to set an ubi volume
+ *                           property.
+ * @property: property to set (%UBI_PROP_DIRECT_WRITE)
+ * @padding: reserved for future, not used, has to be zeroed
+ * @value: value to set
+ */
+struct ubi_set_prop_req {
+       uint8_t  property;
+       uint8_t  padding[7];
+       uint64_t value;
+}  __attribute__ ((packed));
 
 #endif /* __UBI_USER_H__ */