Add pgreadlink() on Windows to read junction points

Add support for reading back information about the symbolic
links we've created with pgsymlink(), which are actually
Junction Points. Just like pgsymlink() can only create directory
symlinks, pgreadlink() can only read directory symlinks.

diff --git a/src/include/port.h b/src/include/port.h
index 2f5abdd33486d22148952fdf4e141c2b95f3798e..7ad464c07dc9417c806bb66511573b3ea82401c8 100644 (file)
--- a/src/include/port.h
+++ b/src/include/port.h
@@ -284,8 +284,11 @@ extern int pgunlink(const char *path);
  */
 #if defined(WIN32) && !defined(__CYGWIN__)
 extern int pgsymlink(const char *oldpath, const char *newpath);
+extern int pgreadlink(const char *path, char *buf, size_t size);
+extern bool pgwin32_is_junction(char *path);
 
 #define symlink(oldpath, newpath)  pgsymlink(oldpath, newpath)
+#define readlink(path, buf, size)  pgreadlink(path, buf, size)
 #endif
 
 extern bool rmtree(const char *path, bool rmtopdir);

diff --git a/src/port/dirmod.c b/src/port/dirmod.c
index 0d373a428bcc301d204c2d9fabcd46a36368d1ae..b6a5564c2c49373a39d2beebffc28836013a734c 100644 (file)
--- a/src/port/dirmod.c
+++ b/src/port/dirmod.c
@@ -297,6 +297,124 @@ pgsymlink(const char *oldpath, const char *newpath)
 
    return 0;
 }
+
+/*
+ * pgreadlink - uses Win32 junction points
+ */
+int
+pgreadlink(const char *path, char *buf, size_t size)
+{
+   DWORD       attr;
+   HANDLE      h;
+   char        buffer[MAX_PATH * sizeof(WCHAR) + sizeof(REPARSE_JUNCTION_DATA_BUFFER)];
+   REPARSE_JUNCTION_DATA_BUFFER *reparseBuf = (REPARSE_JUNCTION_DATA_BUFFER *) buffer;
+   DWORD       len;
+   int         r;
+
+   attr = GetFileAttributes(path);
+   if (attr == INVALID_FILE_ATTRIBUTES)
+   {
+       _dosmaperr(GetLastError());
+       return -1;
+   }
+   if ((attr & FILE_ATTRIBUTE_REPARSE_POINT) == 0)
+   {
+       errno = EINVAL;
+       return -1;
+   }
+
+   h = CreateFile(path,
+                  GENERIC_READ,
+                  FILE_SHARE_READ | FILE_SHARE_WRITE,
+                  NULL,
+                  OPEN_EXISTING,
+                  FILE_FLAG_OPEN_REPARSE_POINT | FILE_FLAG_BACKUP_SEMANTICS,
+                  0);
+   if (h == INVALID_HANDLE_VALUE)
+   {
+       _dosmaperr(GetLastError());
+       return -1;
+   }
+
+   if (!DeviceIoControl(h,
+                        FSCTL_GET_REPARSE_POINT,
+                        NULL,
+                        0,
+                        (LPVOID) reparseBuf,
+                        sizeof(buffer),
+                        &len,
+                        NULL))
+   {
+       LPSTR       msg;
+
+       errno = 0;
+       FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM,
+                     NULL, GetLastError(),
+                     MAKELANGID(LANG_ENGLISH, SUBLANG_DEFAULT),
+                     (LPSTR) &msg, 0, NULL);
+#ifndef FRONTEND
+       ereport(ERROR,
+               (errcode_for_file_access(),
+                errmsg("could not get junction for \"%s\": %s",
+                       path, msg)));
+#else
+       fprintf(stderr, _("could not get junction for \"%s\": %s\n"),
+               path, msg);
+#endif
+       LocalFree(msg);
+       CloseHandle(h);
+       errno = EINVAL;
+       return -1;
+   }
+   CloseHandle(h);
+
+   /* Got it, let's get some results from this */
+   if (reparseBuf->ReparseTag != IO_REPARSE_TAG_MOUNT_POINT)
+   {
+       errno = EINVAL;
+       return -1;
+   }
+
+   r = WideCharToMultiByte(CP_ACP, 0,
+                           reparseBuf->PathBuffer, -1,
+                           buf,
+                           size,
+                           NULL, NULL);
+
+   if (r <= 0)
+   {
+       errno = EINVAL;
+       return -1;
+   }
+
+   /*
+    * If the path starts with "\??\", which it will do in most (all?) cases,
+    * strip those out.
+    */
+   if (r > 4 && strncmp(buf, "\\??\\", 4) == 0)
+   {
+       memmove(buf, buf + 4, strlen(buf + 4) + 1);
+       r -= 4;
+   }
+   return r;
+}
+
+/*
+ * Assumes the file exists, so will return false if it doesn't
+ * (since a nonexistant file is not a junction)
+ */
+bool
+pgwin32_is_junction(char *path)
+{
+   DWORD       attr = GetFileAttributes(path);
+
+   if (attr == INVALID_FILE_ATTRIBUTES)
+   {
+       _dosmaperr(GetLastError());
+       return false;
+   }
+   return ((attr & FILE_ATTRIBUTE_REPARSE_POINT) == FILE_ATTRIBUTE_REPARSE_POINT);
+}
 #endif   /* defined(WIN32) && !defined(__CYGWIN__) */