busybox: add --uninstall option

Add an option to allow hard links to be removed.

   busybox --uninstall file

removes all hard links to the given file (including the file itself.)
Since Microsoft Windows refuses to delete a running executable a
BusyBox binary is unable to remove links to itself.

   busybox --uninstall -n file

displays the names of all hard links to the given file.

Although this feature is couched in terms of uninstalling BusyBox
it's actually quite general:  it can be used to delete or display
hard links to any file.

3 files changed, 72 insertions, 2 deletions

diff --git a/include/mingw.h b/include/mingw.h
index cef53a7c9..b712e4ec0 100644
--- a/include/mingw.h
+++ b/include/mingw.h
@@ -482,3 +482,4 @@ ULONGLONG CompatGetTickCount64(void);
 #define GetTickCount64 CompatGetTickCount64
 
 ssize_t get_random_bytes(void *buf, ssize_t count);
+int enumerate_links(const char *file, char *name);
diff --git a/libbb/appletlib.c b/libbb/appletlib.c
index 11136de11..8a66b3303 100644
--- a/libbb/appletlib.c
+++ b/libbb/appletlib.c
@@ -776,7 +776,8 @@ static void install_links(const char *busybox,
         while (*appname) {
                 fpc = xasprintf("%s/%s.exe", custom_install_dir, appname);
                 rc = link(busybox, fpc);
-                if (rc != 0 && errno != EEXIST) {
+                if (rc != 0 && (errno != EEXIST ||
+                                strcmp("busybox.exe", bb_basename(fpc)) != 0)) {
                         bb_simple_perror_msg(fpc);
                 }
                 free(fpc);
@@ -885,7 +886,13 @@ int busybox_main(int argc UNUSED_PARAM, char **argv)
                         "   or: busybox --show SCRIPT\n"
 #  endif
                         IF_FEATURE_INSTALLER(
-                        "   or: busybox --install "IF_NOT_PLATFORM_MINGW32("[-s] ")"[DIR]\n"
+                        IF_NOT_PLATFORM_MINGW32(
+                        "   or: busybox --install [-s] [DIR]\n"
+                        )
+                        IF_PLATFORM_MINGW32(
+                        "   or: busybox --install [DIR]\n"
+                        "   or: busybox --uninstall [-n] file\n"
+                        )
                         )
                         "   or: function [arguments]...\n"
                         "\n"
@@ -1016,6 +1023,29 @@ int busybox_main(int argc UNUSED_PARAM, char **argv)
                 return 0;
         }
 
+#if ENABLE_PLATFORM_MINGW32 && ENABLE_FEATURE_INSTALLER
+        if (strcmp(argv[1], "--uninstall") == 0) {
+                char name[PATH_MAX];
+                int dry_run = (argv[2] && strcmp(argv[2], "-n") == 0 && ++argv);
+                const char *file = argv[2];
+
+                if (!argv[2])
+                        bb_error_msg_and_die(bb_msg_requires_arg, "--uninstall");
+
+                while (enumerate_links(file, name)) {
+                        if (dry_run) {
+                                full_write1_str(name);
+                                full_write1_str("\n");
+                        }
+                        else if (unlink(name) != 0) {
+                                bb_simple_perror_msg(name);
+                        }
+                        file = NULL;
+                }
+                return 0;
+        }
+#endif
+
         if (strcmp(argv[1], "--help") == 0) {
                 /* "busybox --help [<applet>]" */
                 if (!argv[2])
diff --git a/win32/mingw.c b/win32/mingw.c
index c420992d5..8d1da5199 100644
--- a/win32/mingw.c
+++ b/win32/mingw.c
@@ -1289,3 +1289,42 @@ ULONGLONG CompatGetTickCount64(void)
         return GetTickCount64();
 }
 #endif
+
+#if ENABLE_FEATURE_INSTALLER
+/*
+ * Enumerate the names of all hard links to a file.  The first call
+ * provides the file name as the first argument; subsequent calls must
+ * set the first argument to NULL.  Returns 0 on error or when there are
+ * no more links.
+ */
+int enumerate_links(const char *file, char *name)
+{
+        static HANDLE h = INVALID_HANDLE_VALUE;
+        char aname[PATH_MAX];
+        wchar_t wname[PATH_MAX];
+        DWORD length = PATH_MAX;
+        DECLARE_PROC_ADDR(HANDLE, FindFirstFileNameW, LPCWSTR, DWORD, LPDWORD,
+                                                PWSTR);
+        DECLARE_PROC_ADDR(BOOL, FindNextFileNameW, HANDLE, LPDWORD, PWSTR);
+
+        if (!INIT_PROC_ADDR(kernel32.dll, FindFirstFileNameW) ||
+                        !INIT_PROC_ADDR(kernel32.dll, FindNextFileNameW))
+                return 0;
+
+        if (file != NULL) {
+                wchar_t wfile[PATH_MAX];
+                MultiByteToWideChar(CP_ACP, 0, file, -1, wfile, PATH_MAX);
+                h = FindFirstFileNameW(wfile, 0, &length, wname);
+                if (h == INVALID_HANDLE_VALUE)
+                        return 0;
+        }
+        else if (!FindNextFileNameW(h, &length, wname)) {
+                FindClose(h);
+                h = INVALID_HANDLE_VALUE;
+                return 0;
+        }
+        WideCharToMultiByte(CP_ACP, 0, wname, -1, aname, PATH_MAX, NULL, NULL);
+        realpath(aname, name);
+        return 1;
+}
+#endif