[PATCH V2 0/2] fw_env: two minor code cleanups

[PATCH V2 0/2] fw_env: two minor code cleanups

[Rafał Miłecki]

From: Rafał Miłecki <rafal@milecki.pl>

Hi,

I'm a long time OpenWrt developer and just recently I started working
with some devices using U-Boot.

I was trying to understand how environment variables are read in user
space and I had some problems understanding fw_env_open() logic. I
eventually got it but I thought I may help further developers by
simpliifying its code a bit.

I hope you may find those patches useful and review / apply them.

Rafał Miłecki (2):
  fw_env: make flash_io() take buffer as an argument
  fw_env: simplify logic & code paths in the fw_env_open()

 tools/env/fw_env.c | 105 +++++++++++++++++++--------------------------
 1 file changed, 45 insertions(+), 60 deletions(-)

-- 
2.31.1

[PATCH V2 1/2] fw_env: make flash_io() take buffer as an argument

[Rafał Miłecki]

From: Rafał Miłecki <rafal@milecki.pl>

It's usually easier to understand code & follow it if all arguments are
passed explicitly. Many coding styles also discourage using global
variables.

Behaviour of flash_io() was a bit unintuitive as it was writing to a
buffer referenced in a global struct. That required developers to
remember how it works and sometimes required hacking "environment"
global struct variable to read data into a proper buffer.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
---
V2: Pass correct buffer to the flash_io()
---
 tools/env/fw_env.c | 32 ++++++++++++++++----------------
 1 file changed, 16 insertions(+), 16 deletions(-)

diff --git a/tools/env/fw_env.c b/tools/env/fw_env.c
index 3da75be783..84c88182db 100644
--- a/tools/env/fw_env.c
+++ b/tools/env/fw_env.c
@@ -346,7 +346,7 @@ static int ubi_write(int fd, const void *buf, size_t count)
 	return 0;
 }
 
-static int flash_io(int mode);
+static int flash_io(int mode, void *buf, size_t count);
 static int parse_config(struct env_opts *opts);
 
 #if defined(CONFIG_FILE)
@@ -516,7 +516,7 @@ int fw_env_flush(struct env_opts *opts)
 	*environment.crc = crc32(0, (uint8_t *) environment.data, ENV_SIZE);
 
 	/* write environment back to flash */
-	if (flash_io(O_RDWR)) {
+	if (flash_io(O_RDWR, environment.image, CUR_ENVSIZE)) {
 		fprintf(stderr, "Error: can't write fw_env to flash\n");
 		return -1;
 	}
@@ -1185,7 +1185,8 @@ static int flash_flag_obsolete(int dev, int fd, off_t offset)
 	return rc;
 }
 
-static int flash_write(int fd_current, int fd_target, int dev_target)
+static int flash_write(int fd_current, int fd_target, int dev_target, void *buf,
+		       size_t count)
 {
 	int rc;
 
@@ -1212,11 +1213,10 @@ static int flash_write(int fd_current, int fd_target, int dev_target)
 	if (IS_UBI(dev_target)) {
 		if (ubi_update_start(fd_target, CUR_ENVSIZE) < 0)
 			return -1;
-		return ubi_write(fd_target, environment.image, CUR_ENVSIZE);
+		return ubi_write(fd_target, buf, count);
 	}
 
-	rc = flash_write_buf(dev_target, fd_target, environment.image,
-			     CUR_ENVSIZE);
+	rc = flash_write_buf(dev_target, fd_target, buf, count);
 	if (rc < 0)
 		return rc;
 
@@ -1235,17 +1235,17 @@ static int flash_write(int fd_current, int fd_target, int dev_target)
 	return 0;
 }
 
-static int flash_read(int fd)
+static int flash_read(int fd, void *buf, size_t count)
 {
 	int rc;
 
 	if (IS_UBI(dev_current)) {
 		DEVTYPE(dev_current) = MTD_ABSENT;
 
-		return ubi_read(fd, environment.image, CUR_ENVSIZE);
+		return ubi_read(fd, buf, count);
 	}
 
-	rc = flash_read_buf(dev_current, fd, environment.image, CUR_ENVSIZE,
+	rc = flash_read_buf(dev_current, fd, buf, count,
 			    DEVOFFSET(dev_current));
 	if (rc != CUR_ENVSIZE)
 		return -1;
@@ -1291,7 +1291,7 @@ err:
 	return rc;
 }
 
-static int flash_io_write(int fd_current)
+static int flash_io_write(int fd_current, void *buf, size_t count)
 {
 	int fd_target = -1, rc, dev_target;
 	const char *dname, *target_temp = NULL;
@@ -1322,7 +1322,7 @@ static int flash_io_write(int fd_current)
 			fd_target = fd_current;
 	}
 
-	rc = flash_write(fd_current, fd_target, dev_target);
+	rc = flash_write(fd_current, fd_target, dev_target, buf, count);
 
 	if (fsync(fd_current) && !(errno == EINVAL || errno == EROFS)) {
 		fprintf(stderr,
@@ -1377,7 +1377,7 @@ static int flash_io_write(int fd_current)
 	return rc;
 }
 
-static int flash_io(int mode)
+static int flash_io(int mode, void *buf, size_t count)
 {
 	int fd_current, rc;
 
@@ -1391,9 +1391,9 @@ static int flash_io(int mode)
 	}
 
 	if (mode == O_RDWR) {
-		rc = flash_io_write(fd_current);
+		rc = flash_io_write(fd_current, buf, count);
 	} else {
-		rc = flash_read(fd_current);
+		rc = flash_read(fd_current, buf, count);
 	}
 
 	if (close(fd_current)) {
@@ -1455,7 +1455,7 @@ int fw_env_open(struct env_opts *opts)
 	}
 
 	dev_current = 0;
-	if (flash_io(O_RDONLY)) {
+	if (flash_io(O_RDONLY, environment.image, CUR_ENVSIZE)) {
 		ret = -EIO;
 		goto open_cleanup;
 	}
@@ -1490,7 +1490,7 @@ int fw_env_open(struct env_opts *opts)
 		 * other pointers in environment still point inside addr0
 		 */
 		environment.image = addr1;
-		if (flash_io(O_RDONLY)) {
+		if (flash_io(O_RDONLY, environment.data, CUR_ENVSIZE)) {
 			ret = -EIO;
 			goto open_cleanup;
 		}
-- 
2.31.1

[PATCH V2 2/2] fw_env: simplify logic & code paths in the fw_env_open()

[Rafał Miłecki]

From: Rafał Miłecki <rafal@milecki.pl>

Environment variables can be stored in two formats:
1. Single entry with header containing CRC32
2. Two entries with extra flags field in each entry header

For that reason fw_env_open() has two main code paths and there are
pointers for CRC32/flags/data.

Previous implementation was a bit hard to follow:
1. It was checking for used format twice (in reversed order each time)
2. It was setting "environment" global struct fields to some temporary
   values that required extra comments explaining it

This change simplifies that code:
1. It introduces two clear code paths
2. It sets "environment" global struct fields values only once it really
   knows them

To be fair there are *two* crc32() calls now and an extra pointer
variable but that should be cheap enough and worth it.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
---
V2: Add missing "environment.image = addr0;"
---
 tools/env/fw_env.c | 77 +++++++++++++++++++---------------------------
 1 file changed, 31 insertions(+), 46 deletions(-)

diff --git a/tools/env/fw_env.c b/tools/env/fw_env.c
index 84c88182db..31afef6f3b 100644
--- a/tools/env/fw_env.c
+++ b/tools/env/fw_env.c
@@ -1421,9 +1421,6 @@ int fw_env_open(struct env_opts *opts)
 
 	int ret;
 
-	struct env_image_single *single;
-	struct env_image_redundant *redundant;
-
 	if (!opts)
 		opts = &default_opts;
 
@@ -1439,40 +1436,37 @@ int fw_env_open(struct env_opts *opts)
 		goto open_cleanup;
 	}
 
-	/* read environment from FLASH to local buffer */
-	environment.image = addr0;
-
-	if (have_redund_env) {
-		redundant = addr0;
-		environment.crc = &redundant->crc;
-		environment.flags = &redundant->flags;
-		environment.data = redundant->data;
-	} else {
-		single = addr0;
-		environment.crc = &single->crc;
-		environment.flags = NULL;
-		environment.data = single->data;
-	}
-
 	dev_current = 0;
-	if (flash_io(O_RDONLY, environment.image, CUR_ENVSIZE)) {
+	if (flash_io(O_RDONLY, addr0, CUR_ENVSIZE)) {
 		ret = -EIO;
 		goto open_cleanup;
 	}
 
-	crc0 = crc32(0, (uint8_t *)environment.data, ENV_SIZE);
-
-	crc0_ok = (crc0 == *environment.crc);
 	if (!have_redund_env) {
+		struct env_image_single *single = addr0;
+
+		crc0 = crc32(0, (uint8_t *)single->data, ENV_SIZE);
+		crc0_ok = (crc0 == single->crc);
 		if (!crc0_ok) {
 			fprintf(stderr,
 				"Warning: Bad CRC, using default environment\n");
-			memcpy(environment.data, default_environment,
+			memcpy(single->data, default_environment,
 			       sizeof(default_environment));
 			environment.dirty = 1;
 		}
+
+		environment.image = addr0;
+		environment.crc = &single->crc;
+		environment.flags = NULL;
+		environment.data = single->data;
 	} else {
-		flag0 = *environment.flags;
+		struct env_image_redundant *redundant0 = addr0;
+		struct env_image_redundant *redundant1;
+
+		crc0 = crc32(0, (uint8_t *)redundant0->data, ENV_SIZE);
+		crc0_ok = (crc0 == redundant0->crc);
+
+		flag0 = redundant0->flags;
 
 		dev_current = 1;
 		addr1 = calloc(1, CUR_ENVSIZE);
@@ -1483,14 +1477,9 @@ int fw_env_open(struct env_opts *opts)
 			ret = -ENOMEM;
 			goto open_cleanup;
 		}
-		redundant = addr1;
+		redundant1 = addr1;
 
-		/*
-		 * have to set environment.image for flash_read(), careful -
-		 * other pointers in environment still point inside addr0
-		 */
-		environment.image = addr1;
-		if (flash_io(O_RDONLY, environment.data, CUR_ENVSIZE)) {
+		if (flash_io(O_RDONLY, addr1, CUR_ENVSIZE)) {
 			ret = -EIO;
 			goto open_cleanup;
 		}
@@ -1518,18 +1507,12 @@ int fw_env_open(struct env_opts *opts)
 			goto open_cleanup;
 		}
 
-		crc1 = crc32(0, (uint8_t *)redundant->data, ENV_SIZE);
+		crc1 = crc32(0, (uint8_t *)redundant1->data, ENV_SIZE);
 
-		crc1_ok = (crc1 == redundant->crc);
-		flag1 = redundant->flags;
+		crc1_ok = (crc1 == redundant1->crc);
+		flag1 = redundant1->flags;
 
-		/*
-		 * environment.data still points to ((struct
-		 * env_image_redundant *)addr0)->data. If the two
-		 * environments differ, or one has bad crc, force a
-		 * write-out by marking the environment dirty.
-		 */
-		if (memcmp(environment.data, redundant->data, ENV_SIZE) ||
+		if (memcmp(redundant0->data, redundant1->data, ENV_SIZE) ||
 		    !crc0_ok || !crc1_ok)
 			environment.dirty = 1;
 
@@ -1540,7 +1523,7 @@ int fw_env_open(struct env_opts *opts)
 		} else if (!crc0_ok && !crc1_ok) {
 			fprintf(stderr,
 				"Warning: Bad CRC, using default environment\n");
-			memcpy(environment.data, default_environment,
+			memcpy(redundant0->data, default_environment,
 			       sizeof(default_environment));
 			environment.dirty = 1;
 			dev_current = 0;
@@ -1586,13 +1569,15 @@ int fw_env_open(struct env_opts *opts)
 		 */
 		if (dev_current) {
 			environment.image = addr1;
-			environment.crc = &redundant->crc;
-			environment.flags = &redundant->flags;
-			environment.data = redundant->data;
+			environment.crc = &redundant1->crc;
+			environment.flags = &redundant1->flags;
+			environment.data = redundant1->data;
 			free(addr0);
 		} else {
 			environment.image = addr0;
-			/* Other pointers are already set */
+			environment.crc = &redundant0->crc;
+			environment.flags = &redundant0->flags;
+			environment.data = redundant0->data;
 			free(addr1);
 		}
 #ifdef DEBUG
-- 
2.31.1