mtd: some basic code cleanups

While looking at our exit() invocations I noticed that the mtd_probe
stuff uses 'exit(-1)' at various places, which is not really a good
idea, as exit codes of processes on Linux are supposed to be in the
range of 0…255.

This patch cleans that up a bit, and fixes a number of other things:

1. Let's always let main() exit, nothing intermediary. We generally
   don't like code that invokes exit() on its own.

2. Close the file descriptors opened.

3. Some logging for errors is added, mostly on debug level.

Please review this with extra care. As I don't have the right hardware
to test this patch I only did superficial testing.

systemd-commit: 41b9d436b2739cbe8bf9482b665d85d59d06bc0e
Author: Lennart Poettering <lennart@poettering.net>
Date:   Tue Apr 24 17:50:01 2018 +0200

src/mtd_probe/Makefile.am

@@ -1,7 +1,7 @@
 ACLOCAL_AMFLAGS = -I m4 ${ACLOCAL_FLAGS}
 
 AM_CPPFLAGS = \
-        -I $(top_srcdir)/src/shared
+	-I $(top_srcdir)/src/shared
 
 udevlibexec_PROGRAMS = \
 	mtd_probe
@@ -10,3 +10,7 @@ mtd_probe_SOURCES =  \
 	mtd_probe.c \
 	mtd_probe.h \
 	probe_smartmedia.c
+
+mtd_probe_LDADD = \
+	$(top_builddir)/src/libudev/libudev-private.la \
+	$(top_builddir)/src/udev/libudev-core.la

src/mtd_probe/mtd_probe.c

@@ -31,29 +31,28 @@
 #include <stdlib.h>
 #include "mtd_probe.h"
 
-int main(int argc, char** argv)
-{
-        int mtd_fd;
-        int error;
+int main(int argc, char** argv) {
+        int mtd_fd = -1;
         mtd_info_t mtd_info;
 
         if (argc != 2) {
                 printf("usage: mtd_probe /dev/mtd[n]\n");
-                return 1;
+                return EXIT_FAILURE;
         }
 
         mtd_fd = open(argv[1], O_RDONLY|O_CLOEXEC);
-        if (mtd_fd == -1) {
-                perror("open");
-                exit(-1);
+        if (mtd_fd < 0) {
+                log_error_errno(errno, "Failed to open: %m");
+                return EXIT_FAILURE;
         }
 
-        error = ioctl(mtd_fd, MEMGETINFO, &mtd_info);
-        if (error == -1) {
-                perror("ioctl");
-                exit(-1);
+        if (ioctl(mtd_fd, MEMGETINFO, &mtd_info) < 0) {
+                log_error_errno(errno, "Failed to issue MEMGETINFO ioctl: %m");
+                return EXIT_FAILURE;
         }
 
-        probe_smart_media(mtd_fd, &mtd_info);
-        return -1;
+        if (probe_smart_media(mtd_fd, &mtd_info) < 0)
+                return EXIT_FAILURE;
+
+        return EXIT_SUCCESS;
 }

src/mtd_probe/mtd_probe.h

@@ -48,4 +48,4 @@ struct sm_oob {
 #define SM_SMALL_PAGE                 256
 #define SM_SMALL_OOB_SIZE        8
 
-void probe_smart_media(int mtd_fd, mtd_info_t *info);
+int probe_smart_media(int mtd_fd, mtd_info_t *info);

src/mtd_probe/probe_smartmedia.c

@@ -32,29 +32,32 @@ static const uint8_t cis_signature[] = {
         0x01, 0x03, 0xD9, 0x01, 0xFF, 0x18, 0x02, 0xDF, 0x01, 0x20
 };
 
-
-void probe_smart_media(int mtd_fd, mtd_info_t* info)
-{
+int probe_smart_media(int mtd_fd, mtd_info_t* info) {
         int sector_size;
         int block_size;
         int size_in_megs;
         int spare_count;
-        char* cis_buffer = malloc(SM_SECTOR_SIZE);
+        uint8_t *cis_buffer = NULL;
         int offset;
         int cis_found = 0;
 
+        cis_buffer = malloc(SM_SECTOR_SIZE);
         if (!cis_buffer)
-                return;
+                return log_oom();
 
-        if (info->type != MTD_NANDFLASH)
+        if (info->type != MTD_NANDFLASH) {
+                log_debug("Not marked MTD_NANDFLASH.");
                 goto exit;
+        }
 
         sector_size = info->writesize;
         block_size = info->erasesize;
         size_in_megs = info->size / (1024 * 1024);
 
-        if (sector_size != SM_SECTOR_SIZE && sector_size != SM_SMALL_PAGE)
+        if (!IN_SET(sector_size, SM_SECTOR_SIZE, SM_SMALL_PAGE)) {
+                log_debug("Unexpected sector size: %i", sector_size);
                 goto exit;
+        }
 
         switch(size_in_megs) {
         case 1:
@@ -69,27 +72,30 @@ void probe_smart_media(int mtd_fd, mtd_info_t* info)
                 break;
         }
 
-        for (offset = 0 ; offset < block_size * spare_count ;
-                                                offset += sector_size) {
-                lseek(mtd_fd, SEEK_SET, offset);
-                if (read(mtd_fd, cis_buffer, SM_SECTOR_SIZE) == SM_SECTOR_SIZE){
+        for (offset = 0; offset < block_size * spare_count; offset += sector_size) {
+                (void) lseek(mtd_fd, SEEK_SET, offset);
+
+                if (read(mtd_fd, cis_buffer, SM_SECTOR_SIZE) == SM_SECTOR_SIZE) {
                         cis_found = 1;
                         break;
                 }
         }
 
-        if (!cis_found)
+        if (!cis_found) {
+                log_debug("CIS not found");
                 goto exit;
+        }
 
         if (memcmp(cis_buffer, cis_signature, sizeof(cis_signature)) != 0 &&
-                (memcmp(cis_buffer + SM_SMALL_PAGE, cis_signature,
-                        sizeof(cis_signature)) != 0))
+            memcmp(cis_buffer + SM_SMALL_PAGE, cis_signature, sizeof(cis_signature)) != 0) {
+                log_debug("CIS signature didn't match");
                 goto exit;
+        }
 
         printf("MTD_FTL=smartmedia\n");
         free(cis_buffer);
-        exit(0);
+        return 0;
 exit:
         free(cis_buffer);
-        return;
+        return -1;
 }