[glib/wip/pwithnall/statx: 2/4] glocalfileinfo: Add support for optional/required fields in stat bufs

[Philip Withnall <pwithnall src gnome org>]

commit 622806d5cf18c9eba6438789ba552cee8f3ab712
Author: Andre Miranda <andre42m gmail com>
Date:   Fri Aug 14 15:52:03 2020 +0100

    glocalfileinfo: Add support for optional/required fields in stat bufs
    
    This is a step towards supporting `statx()`, which allows the set of
    fields it returns to be specified by the caller. Currently, the existing
    `stat()` and `fstat()` calls continue to be made, and there are no
    behavioural changes — but the new wrapper functions will be extended in
    future.
    
    Helps: #1970

 gio/glocalfile.c             |  10 ++--
 gio/glocalfileinfo.c         |  37 ++++++--------
 gio/glocalfileinfo.h         | 116 +++++++++++++++++++++++++++++++++++++++++++
 gio/glocalfileoutputstream.c |  33 ++++++------
 4 files changed, 154 insertions(+), 42 deletions(-)
---
diff --git a/gio/glocalfile.c b/gio/glocalfile.c
index 3d3f5735f..f92e6ed20 100644
--- a/gio/glocalfile.c
+++ b/gio/glocalfile.c
@@ -1352,11 +1352,7 @@ g_local_file_read (GFile         *file,
       return NULL;
     }
 
-#ifdef G_OS_WIN32
-  ret = GLIB_PRIVATE_CALL (g_win32_fstat) (fd, &buf);
-#else
-  ret = fstat (fd, &buf);
-#endif
+  ret = g_local_file_fstat (fd, G_LOCAL_FILE_STAT_FIELD_TYPE, G_LOCAL_FILE_STAT_FIELD_ALL, &buf);
 
   if (ret == 0 && S_ISDIR (_g_stat_mode (&buf)))
     {
@@ -2706,7 +2702,9 @@ g_local_file_measure_size_of_file (gint           parent_fd,
     return FALSE;
 
 #if defined (AT_FDCWD)
-  if (fstatat (parent_fd, name->data, &buf, AT_SYMLINK_NOFOLLOW) != 0)
+  if (g_local_file_fstatat (parent_fd, name->data, AT_SYMLINK_NOFOLLOW,
+                            G_LOCAL_FILE_STAT_FIELD_BASIC_STATS, G_LOCAL_FILE_STAT_FIELD_ALL,
+                            &buf) != 0)
     {
       int errsv = errno;
       return g_local_file_measure_size_error (state->flags, errsv, name, error);
diff --git a/gio/glocalfileinfo.c b/gio/glocalfileinfo.c
index 1d1f91c8a..0115a385a 100644
--- a/gio/glocalfileinfo.c
+++ b/gio/glocalfileinfo.c
@@ -123,6 +123,8 @@ _g_local_file_info_create_etag (GLocalFileStat *statbuf)
 {
   glong sec, usec;
 
+  g_return_val_if_fail (_g_stat_has_field (statbuf, G_LOCAL_FILE_STAT_FIELD_MTIME), NULL);
+
 #if defined (G_OS_WIN32)
   sec = statbuf->st_mtim.tv_sec;
   usec = statbuf->st_mtim.tv_nsec / 1000;
@@ -1773,11 +1775,7 @@ _g_local_file_info_get (const char             *basename,
 {
   GFileInfo *info;
   GLocalFileStat statbuf;
-#ifdef S_ISLNK
-  struct stat statbuf2;
-#elif defined (G_OS_WIN32)
-  GWin32PrivateStat statbuf2;
-#endif
+  GLocalFileStat statbuf2;
   int res;
   gboolean stat_ok;
   gboolean is_symlink, symlink_broken;
@@ -1799,11 +1797,10 @@ _g_local_file_info_get (const char             *basename,
       return info;
     }
 
-#ifndef G_OS_WIN32
-  res = g_lstat (path, &statbuf);
-#else
-  res = GLIB_PRIVATE_CALL (g_win32_lstat_utf8) (path, &statbuf);
-#endif
+  res = g_local_file_lstat (path,
+                            G_LOCAL_FILE_STAT_FIELD_BASIC_STATS,
+                            G_LOCAL_FILE_STAT_FIELD_ALL,
+                            &statbuf);
 
   if (res == -1)
     {
@@ -1850,11 +1847,10 @@ _g_local_file_info_get (const char             *basename,
       /* Unless NOFOLLOW was set we default to following symlinks */
       if (!(flags & G_FILE_QUERY_INFO_NOFOLLOW_SYMLINKS))
        {
-#ifndef G_OS_WIN32
-         res = stat (path, &statbuf2);
-#else
-         res = GLIB_PRIVATE_CALL (g_win32_stat_utf8) (path, &statbuf2);
-#endif
+          res = g_local_file_stat (path,
+                                   G_LOCAL_FILE_STAT_FIELD_BASIC_STATS,
+                                   G_LOCAL_FILE_STAT_FIELD_ALL,
+                                   &statbuf2);
 
          /* Report broken links as symlinks */
          if (res != -1)
@@ -2073,14 +2069,11 @@ _g_local_file_info_get_from_fd (int         fd,
   GLocalFileStat stat_buf;
   GFileAttributeMatcher *matcher;
   GFileInfo *info;
-  
-#ifdef G_OS_WIN32
-#define FSTAT GLIB_PRIVATE_CALL (g_win32_fstat)
-#else
-#define FSTAT fstat
-#endif
 
-  if (FSTAT (fd, &stat_buf) == -1)
+  if (g_local_file_fstat (fd,
+                          G_LOCAL_FILE_STAT_FIELD_BASIC_STATS,
+                          G_LOCAL_FILE_STAT_FIELD_ALL,
+                          &stat_buf) == -1)
     {
       int errsv = errno;
 
diff --git a/gio/glocalfileinfo.h b/gio/glocalfileinfo.h
index f3dba9b06..9d744d6d4 100644
--- a/gio/glocalfileinfo.h
+++ b/gio/glocalfileinfo.h
@@ -21,8 +21,11 @@
 #ifndef __G_LOCAL_FILE_INFO_H__
 #define __G_LOCAL_FILE_INFO_H__
 
+#include <fcntl.h>
 #include <gio/gfileinfo.h>
 #include <gio/gfile.h>
+#include <glib/glib-private.h>
+#include <glib/gstdio.h>
 #include <glib/gstdioprivate.h>
 #include <sys/stat.h>
 #include <sys/types.h>
@@ -48,6 +51,119 @@ typedef struct
 #define GLocalFileStat struct stat
 #endif
 
+/* If the system doesn’t have statx() support, emulate it using traditional
+ * stat(). It supports fields %G_LOCAL_FILE_STAT_FIELD_BASIC_STATS only, and
+ * always returns all of them. */
+typedef enum
+{
+  G_LOCAL_FILE_STAT_FIELD_TYPE = (1 << 0),
+  G_LOCAL_FILE_STAT_FIELD_MODE = (1 << 1),
+  G_LOCAL_FILE_STAT_FIELD_NLINK = (1 << 2),
+  G_LOCAL_FILE_STAT_FIELD_UID = (1 << 3),
+  G_LOCAL_FILE_STAT_FIELD_GID = (1 << 4),
+  G_LOCAL_FILE_STAT_FIELD_ATIME = (1 << 5),
+  G_LOCAL_FILE_STAT_FIELD_MTIME = (1 << 6),
+  G_LOCAL_FILE_STAT_FIELD_CTIME = (1 << 7),
+  G_LOCAL_FILE_STAT_FIELD_INO = (1 << 8),
+  G_LOCAL_FILE_STAT_FIELD_SIZE = (1 << 9),
+  G_LOCAL_FILE_STAT_FIELD_BLOCKS = (1 << 10),
+  G_LOCAL_FILE_STAT_FIELD_BTIME = (1 << 11),
+} GLocalFileStatField;
+
+#define G_LOCAL_FILE_STAT_FIELD_BASIC_STATS \
+  (G_LOCAL_FILE_STAT_FIELD_TYPE | G_LOCAL_FILE_STAT_FIELD_MODE | \
+   G_LOCAL_FILE_STAT_FIELD_NLINK | G_LOCAL_FILE_STAT_FIELD_UID | \
+   G_LOCAL_FILE_STAT_FIELD_GID | G_LOCAL_FILE_STAT_FIELD_ATIME | \
+   G_LOCAL_FILE_STAT_FIELD_MTIME | G_LOCAL_FILE_STAT_FIELD_CTIME | \
+   G_LOCAL_FILE_STAT_FIELD_INO | G_LOCAL_FILE_STAT_FIELD_SIZE | \
+   G_LOCAL_FILE_STAT_FIELD_BLOCKS)
+#define G_LOCAL_FILE_STAT_FIELD_ALL (G_LOCAL_FILE_STAT_FIELD_BASIC_STATS | G_LOCAL_FILE_STAT_FIELD_BTIME)
+
+static inline int
+g_local_file_fstat (int                  fd,
+                    GLocalFileStatField  mask,
+                    GLocalFileStatField  mask_required,
+                    GLocalFileStat      *stat_buf)
+{
+  if ((G_LOCAL_FILE_STAT_FIELD_BASIC_STATS & (mask_required & mask)) != (mask_required & mask))
+    {
+      /* Only G_LOCAL_FILE_STAT_FIELD_BASIC_STATS are supported. */
+      errno = ERANGE;
+      return -1;
+    }
+
+#ifdef G_OS_WIN32
+  return GLIB_PRIVATE_CALL (g_win32_fstat) (fd, stat_buf);
+#else
+  return fstat (fd, stat_buf);
+#endif
+}
+
+static inline int
+g_local_file_fstatat (int                  fd,
+                      const char          *path,
+                      int                  flags,
+                      GLocalFileStatField  mask,
+                      GLocalFileStatField  mask_required,
+                      GLocalFileStat      *stat_buf)
+{
+  if ((G_LOCAL_FILE_STAT_FIELD_BASIC_STATS & (mask_required & mask)) != (mask_required & mask))
+    {
+      /* Only G_LOCAL_FILE_STAT_FIELD_BASIC_STATS are supported. */
+      errno = ERANGE;
+      return -1;
+    }
+
+#ifdef G_OS_WIN32
+  /* Currently not supported on Windows */
+  errno = ENOSYS;
+  return -1;
+#else
+  return fstatat (fd, path, stat_buf, flags);
+#endif
+}
+
+static inline int
+g_local_file_lstat (const char          *path,
+                    GLocalFileStatField  mask,
+                    GLocalFileStatField  mask_required,
+                    GLocalFileStat      *stat_buf)
+{
+  if ((G_LOCAL_FILE_STAT_FIELD_BASIC_STATS & (mask_required & mask)) != (mask_required & mask))
+    {
+      /* Only G_LOCAL_FILE_STAT_FIELD_BASIC_STATS are supported. */
+      errno = ERANGE;
+      return -1;
+    }
+
+#ifdef G_OS_WIN32
+  return GLIB_PRIVATE_CALL (g_win32_lstat_utf8) (path, stat_buf);
+#else
+  return g_lstat (path, stat_buf);
+#endif
+}
+
+static inline int
+g_local_file_stat (const char          *path,
+                   GLocalFileStatField  mask,
+                   GLocalFileStatField  mask_required,
+                   GLocalFileStat      *stat_buf)
+{
+  if ((G_LOCAL_FILE_STAT_FIELD_BASIC_STATS & (mask_required & mask)) != (mask_required & mask))
+    {
+      /* Only G_LOCAL_FILE_STAT_FIELD_BASIC_STATS are supported. */
+      errno = ERANGE;
+      return -1;
+    }
+
+#ifdef G_OS_WIN32
+  return GLIB_PRIVATE_CALL (g_win32_stat_utf8) (path, stat_buf);
+#else
+  return stat (path, stat_buf);
+#endif
+}
+
+inline static gboolean  _g_stat_has_field  (const GLocalFileStat *buf, GLocalFileStatField field) { return 
(G_LOCAL_FILE_STAT_FIELD_BASIC_STATS & field) == field; }
 
 #ifndef G_OS_WIN32
 inline static mode_t    _g_stat_mode      (const GLocalFileStat *buf) { return buf->st_mode; }
diff --git a/gio/glocalfileoutputstream.c b/gio/glocalfileoutputstream.c
index 2057e3d3a..aa018a062 100644
--- a/gio/glocalfileoutputstream.c
+++ b/gio/glocalfileoutputstream.c
@@ -424,7 +424,7 @@ _g_local_file_output_stream_really_close (GLocalFileOutputStream *file,
       
 #ifndef G_OS_WIN32             /* Already did the fstat() and close() above on Win32 */
 
-  if (fstat (file->priv->fd, &final_stat) == 0)
+  if (g_local_file_fstat (file->priv->fd, G_LOCAL_FILE_STAT_FIELD_MTIME, G_LOCAL_FILE_STAT_FIELD_ALL, 
&final_stat) == 0)
     file->priv->etag = _g_local_file_info_create_etag (&final_stat);
 
   if (!g_close (file->priv->fd, NULL))
@@ -891,12 +891,15 @@ handle_overwrite_open (const char    *filename,
       g_free (display_name);
       return -1;
     }
-  
-#ifdef G_OS_WIN32
-  res = GLIB_PRIVATE_CALL (g_win32_fstat) (fd, &original_stat);
-#else
-  res = fstat (fd, &original_stat);
-#endif
+
+  res = g_local_file_fstat (fd,
+                            G_LOCAL_FILE_STAT_FIELD_TYPE |
+                            G_LOCAL_FILE_STAT_FIELD_MODE |
+                            G_LOCAL_FILE_STAT_FIELD_UID |
+                            G_LOCAL_FILE_STAT_FIELD_GID |
+                            G_LOCAL_FILE_STAT_FIELD_MTIME |
+                            G_LOCAL_FILE_STAT_FIELD_NLINK,
+                            G_LOCAL_FILE_STAT_FIELD_ALL, &original_stat);
   errsv = errno;
 
   if (res != 0)
@@ -986,11 +989,13 @@ handle_overwrite_open (const char    *filename,
           GLocalFileStat tmp_statbuf;
           int tres;
 
-#ifdef G_OS_WIN32
-          tres = GLIB_PRIVATE_CALL (g_win32_fstat) (tmpfd, &tmp_statbuf);
-#else
-          tres = fstat (tmpfd, &tmp_statbuf);
-#endif
+          tres = g_local_file_fstat (tmpfd,
+                                     G_LOCAL_FILE_STAT_FIELD_TYPE |
+                                     G_LOCAL_FILE_STAT_FIELD_MODE |
+                                     G_LOCAL_FILE_STAT_FIELD_UID |
+                                     G_LOCAL_FILE_STAT_FIELD_GID,
+                                     G_LOCAL_FILE_STAT_FIELD_ALL, &tmp_statbuf);
+
          /* Check that we really needed to change something */
          if (tres != 0 ||
              _g_stat_uid (&original_stat) != _g_stat_uid (&tmp_statbuf) ||
@@ -1014,7 +1019,7 @@ handle_overwrite_open (const char    *filename,
   if (create_backup)
     {
 #if defined(HAVE_FCHOWN) && defined(HAVE_FCHMOD)
-      struct stat tmp_statbuf;      
+      GLocalFileStat tmp_statbuf;
 #endif
       char *backup_filename;
       int bfd;
@@ -1050,7 +1055,7 @@ handle_overwrite_open (const char    *filename,
        * bits for the group same as the protection bits for
        * others. */
 #if defined(HAVE_FCHOWN) && defined(HAVE_FCHMOD)
-      if (fstat (bfd, &tmp_statbuf) != 0)
+      if (g_local_file_fstat (bfd, G_LOCAL_FILE_STAT_FIELD_GID, G_LOCAL_FILE_STAT_FIELD_ALL, &tmp_statbuf) 
!= 0)
        {
          g_set_error_literal (error,
                                G_IO_ERROR,