win32: interpret absolute paths as relative to %SYSTEMDRIVE%

BusyBox contains hardcoded references to absolute paths which
are unique in the *nix world but on Microsoft Windows are
interpreted as being on the current drive.  To make these unique
again consider them to be relative to %SYSTEMDRIVE%.

Support this by adding functions to:

- determine the system drive (not using the environment variable);
- change a process's current directory to the root of the system drive;
- make relative paths absolute before changing directory (if needed).

The following applications have been modified:

- ash references /etc/profile from the system drive;
- dpkg places its data store on and installs files to the system drive;
- rpm installs files to the system drive;
- man looks for configuration files and man pages on the system drive.

See GitHub issue #158.

2 files changed, 27 insertions, 0 deletions

diff --git a/archival/dpkg.c b/archival/dpkg.c
index 8b25cfd47..08f15ad44 100644
--- a/archival/dpkg.c
+++ b/archival/dpkg.c
@@ -1752,6 +1752,10 @@ int dpkg_main(int argc UNUSED_PARAM, char **argv)
         int state_status;
         int status_num;
         int i;
+#if ENABLE_PLATFORM_MINGW32
+        char **ptr, *path;
+        int fd;
+#endif
 #if ENABLE_LONG_OPTS
         static const char dpkg_longopts[] ALIGN1 =
 // FIXME: we use -C non-compatibly, should be:
@@ -1796,6 +1800,26 @@ int dpkg_main(int argc UNUSED_PARAM, char **argv)
                 bb_show_usage();
         }
 
+#if ENABLE_PLATFORM_MINGW32
+        if (opt & OPT_install) {
+                /* add system drive prefix to filenames, if necessary */
+                for (ptr = argv; *ptr; ++ptr) {
+                        *ptr = xabsolute_path(*ptr);
+                }
+        }
+
+        chdir_system_drive();
+
+        /* initialise data store */
+        path = xstrdup("/var/lib/dpkg/info");
+        bb_make_directory(path, -1, FILEUTILS_RECUR);
+        free(path);
+
+        fd = open("/var/lib/dpkg/status", O_RDWR|O_CREAT, 0666);
+        if (fd >= 0)
+                xclose(fd);
+#endif
+
 /*      puts("(Reading database ... xxxxx files and directories installed.)"); */
         index_status_file("/var/lib/dpkg/status");
 
diff --git a/archival/rpm.c b/archival/rpm.c
index 3dd4d4777..c9e8785e2 100644
--- a/archival/rpm.c
+++ b/archival/rpm.c
@@ -303,6 +303,9 @@ static void extract_cpio(int fd, const char *source_rpm)
 
         if (source_rpm != NULL) {
                 /* Binary rpm (it was built from some SRPM), install to root */
+#if ENABLE_PLATFORM_MINGW32
+                if (chdir_system_drive())
+#endif
                 xchdir("/");
         } /* else: SRPM, install to current dir */