[PATCH v2 01/10] fs: give erase() a new erase_type parameter

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

Many managed flashes provide an erase operation, which need not be used
for regular writes, but is provided nonetheless for efficient clearing
of large regions of storage to a fixed bit pattern. The erase type allows
users to specify _why_ the erase operation is done, so the driver or
the core code can choose the most optimal operation.

Existing code is annotated with either ERASE_TO_WRITE for code that is
immediately followed by a write and ERASE_TO_CLEAR for the standalone
erase operations of the shell and fastboot erase command.

Use of an enum allows the future addition of more types, e.g.:

  ERASE_TO_ALL_ZERO: to efficiently implement android sparse all-ones
                     (like util-linux blkdiscard --zeroout)
  ERASE_TO_ALL_ONE: to efficiently implement android sparse all-ones
  ERASE_TO_DISCARD: as alternative to ERASE_TO_CLEAR, when unwritten
                    regions are indeed allowed to have arbitrary content
                     (like util-linux blkdiscard without argument)
  ERASE_TO_SECURE: erase data in a manner appropriate for wiping secrets
                     (like util-linux blkdiscard --secure)

We don't introduce any functional change here yet, as no device yet sets
DEVFS_WRITE_AUTOERASE. This will follow in a separate commit.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
---
v1 -> v2:
  - fix typos in commit message (Sascha)
---
 arch/arm/mach-imx/imx-bbu-external-nand.c |  2 +-
 arch/arm/mach-imx/imx-bbu-internal.c      |  4 ++--
 arch/arm/mach-omap/am33xx_bbu_spi_mlo.c   |  2 +-
 commands/flash.c                          |  2 +-
 commands/nandtest.c                       |  2 +-
 common/bbu.c                              |  2 +-
 common/environment.c                      |  7 ++++--
 common/fastboot.c                         |  2 +-
 common/state/backend_bucket_circular.c    |  2 +-
 drivers/misc/storage-by-uuid.c            |  3 +++
 drivers/usb/gadget/function/dfu.c         |  4 ++--
 fs/devfs-core.c                           |  7 +++++-
 fs/devfs.c                                |  5 ++++-
 fs/fs.c                                   |  4 ++--
 include/driver.h                          | 13 ++++++++++++
 include/fs.h                              | 26 +++++++++++++++++++++--
 lib/libfile.c                             |  2 +-
 17 files changed, 69 insertions(+), 20 deletions(-)

diff --git a/arch/arm/mach-imx/imx-bbu-external-nand.c b/arch/arm/mach-imx/imx-bbu-external-nand.c
index 7523008cdb5a..72c2271ff37a 100644
--- a/arch/arm/mach-imx/imx-bbu-external-nand.c
+++ b/arch/arm/mach-imx/imx-bbu-external-nand.c
@@ -153,7 +153,7 @@ static int imx_bbu_external_nand_update(struct bbu_handler *handler, struct bbu_
 
 		debug("writing %d bytes at 0x%08llx\n", now, nand_offset);
 
-		ret = erase(fd, blocksize, nand_offset);
+		ret = erase(fd, blocksize, nand_offset, ERASE_TO_WRITE);
 		if (ret)
 			goto out;
 
diff --git a/arch/arm/mach-imx/imx-bbu-internal.c b/arch/arm/mach-imx/imx-bbu-internal.c
index 8cdaab5c1676..4190d60d18dd 100644
--- a/arch/arm/mach-imx/imx-bbu-internal.c
+++ b/arch/arm/mach-imx/imx-bbu-internal.c
@@ -108,7 +108,7 @@ static int imx_bbu_write_device(struct imx_internal_bbu_handler *imx_handler,
 	if (imx_bbu_erase_required(imx_handler)) {
 		pr_debug("%s: erasing %s from 0x%08x to 0x%08x\n", __func__,
 				devicefile, offset, image_len);
-		ret = erase(fd, image_len, offset);
+		ret = erase(fd, image_len, offset, ERASE_TO_WRITE);
 		if (ret) {
 			pr_err("erasing %s failed with %s\n", devicefile,
 					strerror(-ret));
@@ -340,7 +340,7 @@ static int imx_bbu_internal_v2_write_nand_dbbt(struct imx_internal_bbu_handler *
 
 		pr_debug("writing %d bytes at 0x%08llx\n", now, offset);
 
-		ret = erase(fd, blocksize, offset);
+		ret = erase(fd, blocksize, offset, ERASE_TO_WRITE);
 		if (ret)
 			goto out;
 
diff --git a/arch/arm/mach-omap/am33xx_bbu_spi_mlo.c b/arch/arm/mach-omap/am33xx_bbu_spi_mlo.c
index 2c58c9ae690e..951c3f8ce099 100644
--- a/arch/arm/mach-omap/am33xx_bbu_spi_mlo.c
+++ b/arch/arm/mach-omap/am33xx_bbu_spi_mlo.c
@@ -71,7 +71,7 @@ static int spi_nor_mlo_handler(struct bbu_handler *handler,
 		goto out;
 	}
 
-	ret = erase(dstfd, ERASE_SIZE_ALL, 0);
+	ret = erase(dstfd, ERASE_SIZE_ALL, 0, ERASE_TO_WRITE);
 	if (ret < 0) {
 		printf("could not erase %s: %m", data->devicefile);
 		goto out1;
diff --git a/commands/flash.c b/commands/flash.c
index 5b7060aeadfb..de3bf65e5059 100644
--- a/commands/flash.c
+++ b/commands/flash.c
@@ -43,7 +43,7 @@ static int do_flerase(int argc, char *argv[])
 		goto out;
 	}
 
-	if (erase(fd, size, start)) {
+	if (erase(fd, size, start, ERASE_TO_CLEAR)) {
 		perror("erase");
 		ret = 1;
 	}
diff --git a/commands/nandtest.c b/commands/nandtest.c
index ba7c87a32eea..bc138646a460 100644
--- a/commands/nandtest.c
+++ b/commands/nandtest.c
@@ -160,7 +160,7 @@ static int erase_and_write(loff_t ofs, unsigned char *data,
 	er.start = ofs;
 	er.length = meminfo.erasesize;
 
-	ret = erase(fd, er.length, er.start);
+	ret = erase(fd, er.length, er.start, ERASE_TO_WRITE);
 	if (ret < 0) {
 		perror("\nerase");
 		printf("Could't not erase flash at 0x%08llx length 0x%08llx.\n",
diff --git a/common/bbu.c b/common/bbu.c
index f71747aa2f6d..9ea8a1a3f247 100644
--- a/common/bbu.c
+++ b/common/bbu.c
@@ -453,7 +453,7 @@ int bbu_std_file_handler(struct bbu_handler *handler,
 		goto err_close;
 	}
 
-	ret = erase(fd, data->len, 0);
+	ret = erase(fd, data->len, 0, ERASE_TO_WRITE);
 	if (ret && ret != -ENOSYS) {
 		printf("erasing %s failed with %s\n", data->devicefile,
 				strerror(-ret));
diff --git a/common/environment.c b/common/environment.c
index 39cad0c16a77..dbf4c2f52365 100644
--- a/common/environment.c
+++ b/common/environment.c
@@ -152,7 +152,10 @@ static inline int protect(int fd, size_t count, unsigned long offset, int prot)
 	return 0;
 }
 
-static inline int erase(int fd, size_t count, unsigned long offset)
+enum erase_type {
+	ERASE_TO_WRITE
+};
+static inline int erase(int fd, size_t count, unsigned long offset, enum erase_type type)
 {
 	return 0;
 }
@@ -380,7 +383,7 @@ int envfs_save(const char *filename, const char *dirname, unsigned flags)
 		goto out;
 	}
 
-	ret = erase(envfd, ERASE_SIZE_ALL, 0);
+	ret = erase(envfd, ERASE_SIZE_ALL, 0, ERASE_TO_WRITE);
 
 	/* ENOSYS and EOPNOTSUPP aren't errors here, many devices don't need it */
 	if (ret && errno != ENOSYS && errno != EOPNOTSUPP) {
diff --git a/common/fastboot.c b/common/fastboot.c
index f8a01dea7a65..d283fc8fc098 100644
--- a/common/fastboot.c
+++ b/common/fastboot.c
@@ -789,7 +789,7 @@ static void cb_erase(struct fastboot *fb, const char *cmd)
 	if (fd < 0)
 		fastboot_tx_print(fb, FASTBOOT_MSG_FAIL, strerror(-fd));
 
-	ret = erase(fd, ERASE_SIZE_ALL, 0);
+	ret = erase(fd, ERASE_SIZE_ALL, 0, ERASE_TO_CLEAR);
 
 	close(fd);
 
diff --git a/common/state/backend_bucket_circular.c b/common/state/backend_bucket_circular.c
index 2ac5bf6a8218..6b5873aa9af1 100644
--- a/common/state/backend_bucket_circular.c
+++ b/common/state/backend_bucket_circular.c
@@ -220,7 +220,7 @@ static int state_mtd_peb_write(struct state_backend_storage_bucket_circular *cir
 static int state_mtd_peb_erase(struct state_backend_storage_bucket_circular *circ)
 {
 	return erase(circ->fd, circ->mtd->erasesize,
-		     (off_t)circ->eraseblock * circ->mtd->erasesize);
+		     (off_t)circ->eraseblock * circ->mtd->erasesize, ERASE_TO_WRITE);
 }
 #endif
 
diff --git a/drivers/misc/storage-by-uuid.c b/drivers/misc/storage-by-uuid.c
index db15b64d7dcf..8b8fd901685e 100644
--- a/drivers/misc/storage-by-uuid.c
+++ b/drivers/misc/storage-by-uuid.c
@@ -126,6 +126,9 @@ static void storage_by_uuid_add_partitions(struct sbu *sbu, struct cdev *rcdev)
 	sbu->cdev.dev = sbu->dev;
 	sbu->cdev.priv = sbu;
 
+	if (rcdev->flags & DEVFS_WRITE_AUTOERASE)
+		sbu->cdev.flags |= DEVFS_WRITE_AUTOERASE;
+
 	ret = devfs_create(&sbu->cdev);
 	if (ret) {
 		dev_err(sbu->dev, "Failed to create cdev: %s\n", strerror(-ret));
diff --git a/drivers/usb/gadget/function/dfu.c b/drivers/usb/gadget/function/dfu.c
index a41ff22dcebc..208e0cd23c29 100644
--- a/drivers/usb/gadget/function/dfu.c
+++ b/drivers/usb/gadget/function/dfu.c
@@ -208,7 +208,7 @@ static void dfu_do_write(struct dfu_work *dw)
 
 	if (prog_erase && (dfu_written + wlen) > dfu_erased) {
 		size = roundup(wlen, dfu_mtdinfo.erasesize);
-		ret = erase(dfufd, size, dfu_erased);
+		ret = erase(dfufd, size, dfu_erased, ERASE_TO_WRITE);
 		dfu_erased += size;
 		if (ret && ret != -ENOSYS) {
 			perror("erase");
@@ -333,7 +333,7 @@ static void dfu_do_copy(struct dfu_work *dw)
 		return;
 	}
 
-	ret = erase(fd, ERASE_SIZE_ALL, 0);
+	ret = erase_flash(fd, ERASE_SIZE_ALL, 0);
 	close(fd);
 	if (ret && ret != -ENOSYS) {
 		perror("erase");
diff --git a/fs/devfs-core.c b/fs/devfs-core.c
index ed445fbd4712..2715193c6956 100644
--- a/fs/devfs-core.c
+++ b/fs/devfs-core.c
@@ -509,6 +509,7 @@ static struct cdev *__devfs_add_partition(struct cdev *cdev,
 	loff_t _end = end ? *end : 0;
 	static struct cdev *new;
 	struct cdev *overlap;
+	unsigned inherited_flags = 0;
 
 	if (cdev_by_name(partinfo->name))
 		return ERR_PTR(-EEXIST);
@@ -551,11 +552,14 @@ static struct cdev *__devfs_add_partition(struct cdev *cdev,
 		return overlap;
 	}
 
+	/* Filter flags that we want to pass along to children */
+	inherited_flags |= cdev->flags & DEVFS_WRITE_AUTOERASE;
+
 	if (IS_ENABLED(CONFIG_MTD) && cdev->mtd) {
 		struct mtd_info *mtd;
 
 		mtd = mtd_add_partition(cdev->mtd, offset, size,
-				partinfo->flags, partinfo->name);
+				partinfo->flags | inherited_flags, partinfo->name);
 		if (IS_ERR(mtd))
 			return (void *)mtd;
 
@@ -571,6 +575,7 @@ static struct cdev *__devfs_add_partition(struct cdev *cdev,
 	new->priv = cdev->priv;
 	new->size = size;
 	new->offset = cdev->offset + offset;
+	new->flags = inherited_flags;
 
 	new->dev = cdev->dev;
 	new->master = cdev;
diff --git a/fs/devfs.c b/fs/devfs.c
index 9dbfa91b1d9f..5feb76cfef86 100644
--- a/fs/devfs.c
+++ b/fs/devfs.c
@@ -61,13 +61,16 @@ static int devfs_lseek(struct device *_dev, FILE *f, loff_t pos)
 }
 
 static int devfs_erase(struct device *_dev, FILE *f, loff_t count,
-		       loff_t offset)
+		       loff_t offset, enum erase_type type)
 {
 	struct cdev *cdev = f->priv;
 
 	if (cdev->flags & DEVFS_PARTITION_READONLY)
 		return -EPERM;
 
+	if ((type == ERASE_TO_WRITE) && (cdev->flags & DEVFS_WRITE_AUTOERASE))
+		return 0;
+
 	if (count + offset > cdev->size)
 		count = cdev->size - offset;
 
diff --git a/fs/fs.c b/fs/fs.c
index 656434f67ffa..5e7e05f4990a 100644
--- a/fs/fs.c
+++ b/fs/fs.c
@@ -600,7 +600,7 @@ loff_t lseek(int fd, loff_t offset, int whence)
 }
 EXPORT_SYMBOL(lseek);
 
-int erase(int fd, loff_t count, loff_t offset)
+int erase(int fd, loff_t count, loff_t offset, enum erase_type type)
 {
 	struct fs_driver *fsdrv;
 	FILE *f = fd_to_file(fd, false);
@@ -621,7 +621,7 @@ int erase(int fd, loff_t count, loff_t offset)
 		assert_command_context();
 
 	if (fsdrv->erase)
-		ret = fsdrv->erase(&f->fsdev->dev, f, count, offset);
+		ret = fsdrv->erase(&f->fsdev->dev, f, count, offset, type);
 	else
 		ret = -ENOSYS;
 
diff --git a/include/driver.h b/include/driver.h
index 2b4db2221a6c..c4067d531cc7 100644
--- a/include/driver.h
+++ b/include/driver.h
@@ -562,6 +562,19 @@ extern struct list_head cdev_list;
 #define DEVFS_PARTITION_BOOTABLE_LEGACY	(1U << 11)
 #define DEVFS_PARTITION_BOOTABLE_ESP	(1U << 12)
 #define DEVFS_PARTITION_FOR_FIXUP	(1U << 13)
+#define DEVFS_WRITE_AUTOERASE		(1U << 14)
+
+/**
+ * cdev_write_requires_erase - Check whether writes must be done to erased blocks
+ * @cdev: pointer to cdev structure
+ *
+ * This function checks if the erase operation is required, so a subsequent
+ * write operation can write all bits.
+ */
+static inline bool cdev_write_requires_erase(const struct cdev *cdev)
+{
+	return !(cdev->flags & DEVFS_WRITE_AUTOERASE);
+}
 
 static inline bool cdev_is_mbr_partitioned(const struct cdev *master)
 {
diff --git a/include/fs.h b/include/fs.h
index f87c4c40273f..f5950a052923 100644
--- a/include/fs.h
+++ b/include/fs.h
@@ -10,6 +10,7 @@
 #include <sys/stat.h>
 #include <driver.h>
 #include <filetype.h>
+#include <linux/bits.h>
 #include <linux/fs.h>
 #include <linux/string.h>
 #include <linux/limits.h>
@@ -38,6 +39,27 @@ typedef struct filep {
 
 #define FS_DRIVER_NO_DEV	1
 
+/**
+ * enum erase_type - Type of erase operation
+ * @ERASE_TO_WRITE: Conduct low-level erase operation to prepare for a write
+ *                  to all or part of the erased regions. This is required
+ *                  for raw flashes, but can be omitted by flashes behind
+ *                  a FTL that autoerases on write (e.g. eMMCs)
+ * @ERASE_TO_CLEAR: Force an erase of the region. When read afterwards,
+ *		    A fixed pattern should result, usually either all-zeroes
+ *		    or all-ones depending on storage technology.
+ *
+ * Many managed flashes provide an erase operation, which need not be used
+ * for regular writes, but is provided nonetheless for efficient clearing
+ * of large regions of storage to a fixed bit pattern. The erase type allows
+ * users to specify _why_ the erase operation is done, so the driver or
+ * the core code can choose the most optimal operation.
+ */
+enum erase_type {
+	ERASE_TO_WRITE,
+	ERASE_TO_CLEAR
+};
+
 struct fs_driver {
 	int (*probe) (struct device *dev);
 
@@ -58,7 +80,7 @@ struct fs_driver {
 
 	int (*ioctl)(struct device *dev, FILE *f, unsigned int request, void *buf);
 	int (*erase)(struct device *dev, FILE *f, loff_t count,
-			loff_t offset);
+			loff_t offset, enum erase_type type);
 	int (*protect)(struct device *dev, FILE *f, size_t count,
 			loff_t offset, int prot);
 	int (*discard_range)(struct device *dev, FILE *f, loff_t count,
@@ -127,7 +149,7 @@ int umount_by_cdev(struct cdev *cdev);
 
 /* not-so-standard functions */
 #define ERASE_SIZE_ALL	((loff_t) - 1)
-int erase(int fd, loff_t count, loff_t offset);
+int erase(int fd, loff_t count, loff_t offset, enum erase_type type);
 int protect(int fd, size_t count, loff_t offset, int prot);
 int discard_range(int fd, loff_t count, loff_t offset);
 int protect_file(const char *file, int prot);
diff --git a/lib/libfile.c b/lib/libfile.c
index a34e011f4f7c..80d4591dd6e5 100644
--- a/lib/libfile.c
+++ b/lib/libfile.c
@@ -412,7 +412,7 @@ int write_file_flash(const char *filename, const void *buf, size_t size)
 	if (fd < 0)
 		return fd;
 
-	ret = erase(fd, size, 0);
+	ret = erase(fd, size, 0, ERASE_TO_WRITE);
 	if (ret < 0)
 		goto out_close;
 
-- 
2.39.2