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.

6 files changed, 112 insertions, 1 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 */
 
diff --git a/include/mingw.h b/include/mingw.h
index 7c9423cad..d77a9beb9 100644
--- a/include/mingw.h
+++ b/include/mingw.h
@@ -525,3 +525,6 @@ void hide_console(void);
 
 int unc_root_len(const char *dir);
 int root_len(const char *path);
+char *get_system_drive(void);
+int chdir_system_drive(void);
+char *xabsolute_path(char *path);
diff --git a/miscutils/man.c b/miscutils/man.c
index 3c1a79085..0bc11e623 100644
--- a/miscutils/man.c
+++ b/miscutils/man.c
@@ -253,11 +253,22 @@ int man_main(int argc UNUSED_PARAM, char **argv)
         int cur_mp;
         int opt, not_found;
         char *token[2];
+#if ENABLE_PLATFORM_MINGW32
+        char **ptr;
+#endif
 
         INIT_G();
 
         opt = getopt32(argv, "^+" "aw" "\0" "-1"/*at least one arg*/);
         argv += optind;
+#if ENABLE_PLATFORM_MINGW32
+        /* add system drive prefix to filenames, if necessary */
+        for (ptr = argv; *ptr; ++ptr) {
+                if (strchr(*ptr, '/') || strchr(*ptr, '\\'))
+                        *ptr = xabsolute_path(*ptr);
+        }
+        chdir_system_drive();
+#endif
 
         sec_list = xstrdup("0p:1:1p:2:3:3p:4:5:6:7:8:9");
 
@@ -311,7 +322,8 @@ int man_main(int argc UNUSED_PARAM, char **argv)
                 char *relpath = concat_path_file(dirname(exepath), "man");
                 if (count_mp == 0) {
                         /* default must match path set above */
-                        man_path_list = add_MANPATH(man_path_list, &count_mp, "/usr/man");
+                        man_path_list = add_MANPATH(man_path_list, &count_mp,
+                                                                                (char *)"/usr/man");
                 }
                 man_path_list = add_MANPATH(man_path_list, &count_mp, relpath);
                 free(relpath);
diff --git a/shell/ash.c b/shell/ash.c
index 34ddc14f1..40965bafa 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -14906,6 +14906,9 @@ int ash_main(int argc UNUSED_PARAM, char **argv)
         struct jmploc jmploc;
         struct stackmark smark;
         int login_sh;
+#if ENABLE_PLATFORM_MINGW32
+        char *sd;
+#endif
 
         /* Initialize global data */
         INIT_G_misc();
@@ -15014,6 +15017,16 @@ int ash_main(int argc UNUSED_PARAM, char **argv)
 #endif
 
                 state = 1;
+#if ENABLE_PLATFORM_MINGW32
+                sd = get_system_drive();
+                if (sd) {
+                        char *path = xasprintf("%s/etc/profile", sd);
+                        read_profile(path);
+                        free(sd);
+                        free(path);
+                }
+                else
+#endif
                 read_profile("/etc/profile");
  state1:
                 state = 2;
diff --git a/win32/mingw.c b/win32/mingw.c
index 3ee1a2496..1d5644f92 100644
--- a/win32/mingw.c
+++ b/win32/mingw.c
@@ -1644,3 +1644,59 @@ int root_len(const char *path)
                 return 2;
         return unc_root_len(path);
 }
+
+char *get_system_drive(void)
+{
+        struct passwd *pwd;
+        char *drive = NULL;
+        int len;
+
+        pwd = getpwuid(0);
+        if (pwd != NULL && (len=root_len(pwd->pw_dir))) {
+                drive = xstrdup(pwd->pw_dir);
+                drive[len] = '\0';
+        }
+
+        return drive;
+}
+
+int chdir_system_drive(void)
+{
+        char *sd = get_system_drive();
+        int ret = -1;
+
+        if (sd) {
+                strcat(sd, "/");
+                ret = chdir(sd);
+        }
+        free(sd);
+        return ret;
+}
+
+/*
+ * This function is used to make relative paths absolute before a call
+ * to chdir_system_drive().  It's unlikely to be useful in other cases.
+ *
+ * If the argument is an absolute path or a relative path which resolves
+ * to a path on the system drive return 'path'.  If it's a relative path
+ * which resolves to a path that isn't on the system drive return an
+ * allocated string containing the resolved path.  Die on failure,
+ * which is most likely because the file doesn't exist.
+ */
+char *xabsolute_path(char *path)
+{
+        char *rpath, *sd;
+
+        if (root_len(path) != 0)
+                return path;    // absolute path
+        rpath = xmalloc_realpath(path);
+        if (rpath) {
+                sd = auto_string(get_system_drive());
+                if (sd && is_prefixed_with_case(rpath, sd)) {
+                        free(rpath);
+                        return path;    // resolved path is on system drive
+                }
+                return rpath;
+        }
+        bb_perror_msg_and_die("can't open '%s'", path);
+}