jn: new applet

Add a Windows-specific applet to create a directory junction.

Usage:  jn DIR JUNC

where DIR must be an existing directory on a local drive and JUNC
must not currently exist.

There isn't a simple WIN32 API to create directory junctions.
The implementation of mklink in ReactOS provided useful inspiration.

5 files changed, 172 insertions, 1 deletions

diff --git a/configs/mingw32_defconfig b/configs/mingw32_defconfig
index 65465e81b..78e359500 100644
--- a/configs/mingw32_defconfig
+++ b/configs/mingw32_defconfig
@@ -816,6 +816,7 @@ CONFIG_FEATURE_CROND_DIR=""
 # CONFIG_I2CTRANSFER is not set
 CONFIG_ICONV=y
 CONFIG_INOTIFYD=y
+CONFIG_JN=y
 CONFIG_LESS=y
 CONFIG_FEATURE_LESS_MAXLINES=9999999
 CONFIG_FEATURE_LESS_BRACKETS=y
diff --git a/configs/mingw64_defconfig b/configs/mingw64_defconfig
index bd8750e98..c88da8007 100644
--- a/configs/mingw64_defconfig
+++ b/configs/mingw64_defconfig
@@ -816,6 +816,7 @@ CONFIG_FEATURE_CROND_DIR=""
 # CONFIG_I2CTRANSFER is not set
 CONFIG_ICONV=y
 CONFIG_INOTIFYD=y
+CONFIG_JN=y
 CONFIG_LESS=y
 CONFIG_FEATURE_LESS_MAXLINES=9999999
 CONFIG_FEATURE_LESS_BRACKETS=y
diff --git a/include/mingw.h b/include/mingw.h
index 5e01b874e..b91fbb531 100644
--- a/include/mingw.h
+++ b/include/mingw.h
@@ -479,6 +479,7 @@ NOIMPL(setuid,uid_t gid UNUSED_PARAM);
 NOIMPL(seteuid,uid_t gid UNUSED_PARAM);
 unsigned int sleep(unsigned int seconds);
 int symlink(const char *target, const char *linkpath);
+int create_junction(const char *oldpath, const char *newpath);
 long sysconf(int name);
 IMPL(getpagesize,int,4096,void);
 NOIMPL(ttyname_r,int fd UNUSED_PARAM, char *buf UNUSED_PARAM, int sz UNUSED_PARAM);
diff --git a/miscutils/jn.c b/miscutils/jn.c
new file mode 100644
index 000000000..db6a3e6d9
--- /dev/null
+++ b/miscutils/jn.c
@@ -0,0 +1,37 @@
+/*
+ * directory junction creation for busybox
+ *
+ * Copyright (C) 2017 Denys Vlasenko <vda.linux@googlemail.com>
+ * Copyright (C) 2022 Ron Yorston <rmy@pobox.com>
+ *
+ * Licensed under GPLv2, see file LICENSE in this source tree.
+ */
+//config:config JN
+//config:       bool "jn (3.2 kb)"
+//config:       default y
+//config:       depends on PLATFORM_MINGW32
+//config:       help
+//config:       Creates a directory junction.
+
+//applet:IF_JN(APPLET_NOEXEC(jn, jn, BB_DIR_USR_BIN, BB_SUID_DROP, jn))
+
+//kbuild:lib-$(CONFIG_JN) += jn.o
+
+//usage:#define jn_trivial_usage
+//usage:       "DIR JUNC"
+//usage:#define jn_full_usage "\n\n"
+//usage:       "Create directory junction JUNC to DIR"
+
+#include "libbb.h"
+
+int jn_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
+int jn_main(int argc UNUSED_PARAM, char **argv)
+{
+        getopt32(argv, "^" "" "\0" "=2");
+        argv += optind;
+        if (create_junction(argv[0], argv[1]) != 0) {
+                bb_perror_msg_and_die("can't create junction '%s' to '%s'",
+                        argv[1], argv[0]);
+        }
+        return EXIT_SUCCESS;
+}
diff --git a/win32/mingw.c b/win32/mingw.c
index c35b1d6af..79aaa86f1 100644
--- a/win32/mingw.c
+++ b/win32/mingw.c
@@ -1285,6 +1285,138 @@ int symlink(const char *target, const char *linkpath)
         return 0;
 }
 
+/* Create a directory junction */
+#define MRPB rptr->MountPointReparseBuffer
+#if 0
+static void print_junction(REPARSE_DATA_BUFFER *rptr)
+{
+        int i;
+#define MRPB_HEADER_SIZE \
+        (FIELD_OFFSET(REPARSE_DATA_BUFFER, MountPointReparseBuffer.PathBuffer) - \
+        FIELD_OFFSET(REPARSE_DATA_BUFFER, MountPointReparseBuffer))
+
+        fprintf(stderr, "---\n");
+        fprintf(stderr, "Tag: %lx\n", rptr->ReparseTag);
+        fprintf(stderr, "ReparseDataLength: %d (%d + %d + %d + %d + %d = %d)\n",
+                        rptr->ReparseDataLength, MRPB_HEADER_SIZE,
+                        MRPB.SubstituteNameLength, sizeof(WCHAR),
+                        MRPB.PrintNameLength, sizeof(WCHAR),
+                        MRPB_HEADER_SIZE + MRPB.SubstituteNameLength + sizeof(WCHAR) +
+                                MRPB.PrintNameLength + sizeof(WCHAR));
+        fprintf(stderr, "Reserved: %d\n", rptr->Reserved);
+        fprintf(stderr, "---\n");
+        fprintf(stderr, "SubstituteNameOffset: %d\n", MRPB.SubstituteNameOffset);
+        fprintf(stderr, "SubstituteNameLength: %d\n", MRPB.SubstituteNameLength);
+        fprintf(stderr, "PrintNameOffset: %d\n", MRPB.PrintNameOffset);
+        fprintf(stderr, "PrintNameLength: %d\n", MRPB.PrintNameLength);
+        fprintf(stderr, "SubstituteName: ");
+        for (i = 0; i < MRPB.SubstituteNameLength/sizeof(WCHAR); i++)
+                fprintf(stderr, "%c",
+                        MRPB.PathBuffer[MRPB.SubstituteNameOffset/sizeof(WCHAR) + i]);
+        fprintf(stderr, " (%x)",
+                MRPB.PathBuffer[MRPB.SubstituteNameOffset/sizeof(WCHAR) + i]);
+        fprintf(stderr, "\n");
+        fprintf(stderr, "PrintName:      ");
+        for (i = 0; i < MRPB.PrintNameLength/sizeof(WCHAR); i++)
+                fprintf(stderr, "%c",
+                        MRPB.PathBuffer[MRPB.PrintNameOffset/sizeof(WCHAR) + i]);
+        fprintf(stderr, " (%x)",
+                MRPB.PathBuffer[MRPB.PrintNameOffset/sizeof(WCHAR) + i]);
+        fprintf(stderr, "\n");
+        fprintf(stderr, "---\n");
+}
+#endif
+
+static REPARSE_DATA_BUFFER *make_junction_data_buffer(char *rpath)
+{
+        WCHAR pbuf[PATH_MAX];
+        int plen, slen, rbufsize;
+        REPARSE_DATA_BUFFER *rptr;
+
+        /* We need two strings for the reparse data.  The PrintName is the
+         * target path in Win32 format, the SubstituteName is the same in
+         * NT format. */
+        slash_to_bs(rpath);
+        plen = MultiByteToWideChar(CP_ACP, 0, rpath, -1, pbuf, PATH_MAX);
+        if (plen == 0) {
+                errno = err_win_to_posix();
+                return NULL;
+        }
+        slen = plen + 4;
+
+        rbufsize = (slen + plen + 2) * sizeof(WCHAR) +
+                FIELD_OFFSET(REPARSE_DATA_BUFFER, MountPointReparseBuffer.PathBuffer);
+        rptr = xzalloc(rbufsize);
+
+        rptr->ReparseTag = IO_REPARSE_TAG_MOUNT_POINT;
+        rptr->ReparseDataLength = rbufsize -
+                FIELD_OFFSET(REPARSE_DATA_BUFFER, MountPointReparseBuffer);
+        /* rptr->Reserved = 0; */
+        /* MRPB.SubstituteNameOffset = 0; */
+        MRPB.SubstituteNameLength = slen * sizeof(WCHAR);
+        MRPB.PrintNameOffset = MRPB.SubstituteNameLength + sizeof(WCHAR);
+        MRPB.PrintNameLength = plen * sizeof(WCHAR);
+
+        wcscpy(MRPB.PathBuffer, L"\\??\\");
+        wcscpy(MRPB.PathBuffer + 4, pbuf);
+        wcscpy(MRPB.PathBuffer + slen + 1, pbuf);
+        return rptr;
+}
+
+int create_junction(const char *oldpath, const char *newpath)
+{
+        char rpath[PATH_MAX];
+        struct stat statbuf;
+        REPARSE_DATA_BUFFER *rptr = NULL;
+        HANDLE h;
+        int error = 0;
+        DWORD bytes;
+
+        if (realpath(oldpath, rpath) == NULL || stat(rpath, &statbuf) < 0)
+                return -1;
+
+        if (!has_dos_drive_prefix(rpath)) {
+                errno = EINVAL;
+                return -1;
+        }
+
+        if (!S_ISDIR(statbuf.st_mode)) {
+                errno = ENOTDIR;
+                return -1;
+        }
+
+        if (!(rptr = make_junction_data_buffer(rpath))) {
+                return -1;
+        }
+
+        if (mkdir(newpath, 0777) < 0) {
+                free(rptr);
+                return -1;
+        }
+
+        h = CreateFileA(newpath, GENERIC_READ | GENERIC_WRITE, 0, NULL,
+                        OPEN_EXISTING,
+                        FILE_FLAG_OPEN_REPARSE_POINT | FILE_FLAG_BACKUP_SEMANTICS, NULL);
+        if (h != INVALID_HANDLE_VALUE) {
+                if (DeviceIoControl(h, FSCTL_SET_REPARSE_POINT, rptr,
+                                rptr->ReparseDataLength + REPARSE_DATA_BUFFER_HEADER_SIZE,
+                                NULL, 0, &bytes, NULL) != 0) {
+                        CloseHandle(h);
+                        free(rptr);
+                        return 0;
+                }
+                error = err_win_to_posix();
+                CloseHandle(h);
+        } else {
+                error = err_win_to_posix();
+        }
+
+        rmdir(newpath);
+        free(rptr);
+        errno = error;
+        return -1;
+}
+
 static char *normalize_ntpathA(char *buf)
 {
         /* fix absolute path prefixes */
@@ -1399,7 +1531,6 @@ static wchar_t *normalize_ntpath(wchar_t *wbuf)
 }
 
 #define SRPB rptr->SymbolicLinkReparseBuffer
-#define MRPB rptr->MountPointReparseBuffer
 ssize_t readlink(const char *pathname, char *buf, size_t bufsiz)
 {
         HANDLE h;