UBI: Add initial support for scatter gather

Adds a new set of functions to deal with scatter gather.
ubi_eba_read_leb_sg() will read from a LEB into a scatter gather list.
The new data structure struct ubi_sgl will be used within UBI to
hold the scatter gather list itself and metadata to have a cursor
within the list.

Signed-off-by: Richard Weinberger <richard@nod.at>
Tested-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Reviewed-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>

drivers/mtd/ubi/eba.c

@@ -479,6 +479,61 @@ int ubi_eba_read_leb(struct ubi_device *ubi, struct ubi_volume *vol, int lnum,
 	return err;
 }
 
+/**
+ * ubi_eba_read_leb_sg - read data into a scatter gather list.
+ * @ubi: UBI device description object
+ * @vol: volume description object
+ * @lnum: logical eraseblock number
+ * @sgl: UBI scatter gather list to store the read data
+ * @offset: offset from where to read
+ * @len: how many bytes to read
+ * @check: data CRC check flag
+ *
+ * This function works exactly like ubi_eba_read_leb(). But instead of
+ * storing the read data into a buffer it writes to an UBI scatter gather
+ * list.
+ */
+int ubi_eba_read_leb_sg(struct ubi_device *ubi, struct ubi_volume *vol,
+			struct ubi_sgl *sgl, int lnum, int offset, int len,
+			int check)
+{
+	int to_read;
+	int ret;
+	struct scatterlist *sg;
+
+	for (;;) {
+		ubi_assert(sgl->list_pos < UBI_MAX_SG_COUNT);
+		sg = &sgl->sg[sgl->list_pos];
+		if (len < sg->length - sgl->page_pos)
+			to_read = len;
+		else
+			to_read = sg->length - sgl->page_pos;
+
+		ret = ubi_eba_read_leb(ubi, vol, lnum,
+				       sg_virt(sg) + sgl->page_pos, offset,
+				       to_read, check);
+		if (ret < 0)
+			return ret;
+
+		offset += to_read;
+		len -= to_read;
+		if (!len) {
+			sgl->page_pos += to_read;
+			if (sgl->page_pos == sg->length) {
+				sgl->list_pos++;
+				sgl->page_pos = 0;
+			}
+
+			break;
+		}
+
+		sgl->list_pos++;
+		sgl->page_pos = 0;
+	}
+
+	return ret;
+}
+
 /**
  * recover_peb - recover from write failure.
  * @ubi: UBI device description object

drivers/mtd/ubi/kapi.c

@@ -365,6 +365,43 @@ void ubi_close_volume(struct ubi_volume_desc *desc)
 }
 EXPORT_SYMBOL_GPL(ubi_close_volume);
 
+/**
+ * leb_read_sanity_check - does sanity checks on read requests.
+ * @desc: volume descriptor
+ * @lnum: logical eraseblock number to read from
+ * @offset: offset within the logical eraseblock to read from
+ * @len: how many bytes to read
+ *
+ * This function is used by ubi_leb_read() and ubi_leb_read_sg()
+ * to perform sanity checks.
+ */
+static int leb_read_sanity_check(struct ubi_volume_desc *desc, int lnum,
+				 int offset, int len)
+{
+	struct ubi_volume *vol = desc->vol;
+	struct ubi_device *ubi = vol->ubi;
+	int vol_id = vol->vol_id;
+
+	if (vol_id < 0 || vol_id >= ubi->vtbl_slots || lnum < 0 ||
+	    lnum >= vol->used_ebs || offset < 0 || len < 0 ||
+	    offset + len > vol->usable_leb_size)
+		return -EINVAL;
+
+	if (vol->vol_type == UBI_STATIC_VOLUME) {
+		if (vol->used_ebs == 0)
+			/* Empty static UBI volume */
+			return 0;
+		if (lnum == vol->used_ebs - 1 &&
+		    offset + len > vol->last_eb_bytes)
+			return -EINVAL;
+	}
+
+	if (vol->upd_marker)
+		return -EBADF;
+
+	return 0;
+}
+
 /**
  * ubi_leb_read - read data.
  * @desc: volume descriptor
@@ -401,22 +438,10 @@ int ubi_leb_read(struct ubi_volume_desc *desc, int lnum, char *buf, int offset,
 
 	dbg_gen("read %d bytes from LEB %d:%d:%d", len, vol_id, lnum, offset);
 
-	if (vol_id < 0 || vol_id >= ubi->vtbl_slots || lnum < 0 ||
-	    lnum >= vol->used_ebs || offset < 0 || len < 0 ||
-	    offset + len > vol->usable_leb_size)
-		return -EINVAL;
+	err = leb_read_sanity_check(desc, lnum, offset, len);
+	if (err < 0)
+		return err;
 
-	if (vol->vol_type == UBI_STATIC_VOLUME) {
-		if (vol->used_ebs == 0)
-			/* Empty static UBI volume */
-			return 0;
-		if (lnum == vol->used_ebs - 1 &&
-		    offset + len > vol->last_eb_bytes)
-			return -EINVAL;
-	}
-
-	if (vol->upd_marker)
-		return -EBADF;
 	if (len == 0)
 		return 0;
 
@@ -430,6 +455,46 @@ int ubi_leb_read(struct ubi_volume_desc *desc, int lnum, char *buf, int offset,
 }
 EXPORT_SYMBOL_GPL(ubi_leb_read);
 
+
+/**
+ * ubi_leb_read_sg - read data into a scatter gather list.
+ * @desc: volume descriptor
+ * @lnum: logical eraseblock number to read from
+ * @buf: buffer where to store the read data
+ * @offset: offset within the logical eraseblock to read from
+ * @len: how many bytes to read
+ * @check: whether UBI has to check the read data's CRC or not.
+ *
+ * This function works exactly like ubi_leb_read_sg(). But instead of
+ * storing the read data into a buffer it writes to an UBI scatter gather
+ * list.
+ */
+int ubi_leb_read_sg(struct ubi_volume_desc *desc, int lnum, struct ubi_sgl *sgl,
+		    int offset, int len, int check)
+{
+	struct ubi_volume *vol = desc->vol;
+	struct ubi_device *ubi = vol->ubi;
+	int err, vol_id = vol->vol_id;
+
+	dbg_gen("read %d bytes from LEB %d:%d:%d", len, vol_id, lnum, offset);
+
+	err = leb_read_sanity_check(desc, lnum, offset, len);
+	if (err < 0)
+		return err;
+
+	if (len == 0)
+		return 0;
+
+	err = ubi_eba_read_leb_sg(ubi, vol, sgl, lnum, offset, len, check);
+	if (err && mtd_is_eccerr(err) && vol->vol_type == UBI_STATIC_VOLUME) {
+		ubi_warn(ubi, "mark volume %d as corrupted", vol_id);
+		vol->corrupted = 1;
+	}
+
+	return err;
+}
+EXPORT_SYMBOL_GPL(ubi_leb_read_sg);
+
 /**
  * ubi_leb_write - write data.
  * @desc: volume descriptor

drivers/mtd/ubi/ubi.h

@@ -795,6 +795,9 @@ int ubi_eba_unmap_leb(struct ubi_device *ubi, struct ubi_volume *vol,
 		      int lnum);
 int ubi_eba_read_leb(struct ubi_device *ubi, struct ubi_volume *vol, int lnum,
 		     void *buf, int offset, int len, int check);
+int ubi_eba_read_leb_sg(struct ubi_device *ubi, struct ubi_volume *vol,
+			struct ubi_sgl *sgl, int lnum, int offset, int len,
+			int check);
 int ubi_eba_write_leb(struct ubi_device *ubi, struct ubi_volume *vol, int lnum,
 		      const void *buf, int offset, int len);
 int ubi_eba_write_leb_st(struct ubi_device *ubi, struct ubi_volume *vol,

include/linux/mtd/ubi.h

@@ -23,11 +23,18 @@
 
 #include <linux/ioctl.h>
 #include <linux/types.h>
+#include <linux/scatterlist.h>
 #include <mtd/ubi-user.h>
 
 /* All voumes/LEBs */
 #define UBI_ALL -1
 
+/*
+ * Maximum number of scatter gather list entries,
+ * we use only 64 to have a lower memory foot print.
+ */
+#define UBI_MAX_SG_COUNT 64
+
 /*
  * enum ubi_open_mode - UBI volume open mode constants.
  *
@@ -118,6 +125,35 @@ struct ubi_volume_info {
 	dev_t cdev;
 };
 
+/**
+ * struct ubi_sgl - UBI scatter gather list data structure.
+ * @list_pos: current position in @sg[]
+ * @page_pos: current position in @sg[@list_pos]
+ * @sg: the scatter gather list itself
+ *
+ * ubi_sgl is a wrapper around a scatter list which keeps track of the
+ * current position in the list and the current list item such that
+ * it can be used across multiple ubi_leb_read_sg() calls.
+ */
+struct ubi_sgl {
+	int list_pos;
+	int page_pos;
+	struct scatterlist sg[UBI_MAX_SG_COUNT];
+};
+
+/**
+ * ubi_sgl_init - initialize an UBI scatter gather list data structure.
+ * @usgl: the UBI scatter gather struct itself
+ *
+ * Please note that you still have to use sg_init_table() or any adequate
+ * function to initialize the unterlaying struct scatterlist.
+ */
+static inline void ubi_sgl_init(struct ubi_sgl *usgl)
+{
+	usgl->list_pos = 0;
+	usgl->page_pos = 0;
+}
+
 /**
  * struct ubi_device_info - UBI device description data structure.
  * @ubi_num: ubi device number
@@ -213,6 +249,8 @@ int ubi_unregister_volume_notifier(struct notifier_block *nb);
 void ubi_close_volume(struct ubi_volume_desc *desc);
 int ubi_leb_read(struct ubi_volume_desc *desc, int lnum, char *buf, int offset,
 		 int len, int check);
+int ubi_leb_read_sg(struct ubi_volume_desc *desc, int lnum, struct ubi_sgl *sgl,
+		   int offset, int len, int check);
 int ubi_leb_write(struct ubi_volume_desc *desc, int lnum, const void *buf,
 		  int offset, int len);
 int ubi_leb_change(struct ubi_volume_desc *desc, int lnum, const void *buf,
@@ -233,4 +271,14 @@ static inline int ubi_read(struct ubi_volume_desc *desc, int lnum, char *buf,
 {
 	return ubi_leb_read(desc, lnum, buf, offset, len, 0);
 }
+
+/*
+ * This function is the same as the 'ubi_leb_read_sg()' function, but it does
+ * not provide the checking capability.
+ */
+static inline int ubi_read_sg(struct ubi_volume_desc *desc, int lnum,
+			      struct ubi_sgl *sgl, int offset, int len)
+{
+	return ubi_leb_read_sg(desc, lnum, sgl, offset, len, 0);
+}
 #endif /* !__LINUX_UBI_H__ */