insert-file-contents st_size cleanup

* src/fileio.c (Finsert_file_contents): Store st_size,
not file_size_hint, into current_buffer->modtime_size,
since modtime_size is compared to a later st_size, not
to the actual file size.  Simplify buffer overflow detection
from file size, since this occurred only on regular files.

(cherry picked from commit 8d83402edc96b5a88096ae707241f4e8cb59691b)

diff --git a/src/buffer.h b/src/buffer.h
index 5ecd43c809a34ca956f447338730278222574e9d..5d8162145693f83f6d48737986d35b5917905477 100644 (file)
--- a/src/buffer.h
+++ b/src/buffer.h
@@ -643,11 +643,12 @@ struct buffer
      in no case complain about any mismatch on next save attempt.  */
   struct timespec modtime;
 
-  /* Size of the file when modtime was set.  This is used to detect the
-     case where the file grew while we were reading it, so the modtime
-     is still the same (since it's rounded up to seconds) but we're actually
-     not up-to-date.  -1 means the size is unknown.  Only meaningful if
-     modtime is actually set.  */
+  /* Size of the file when modtime was set.  This is used to detect when
+     the file size changed while we were reading the file, but the
+     modtime is still the same (since it's truncated to clock resolution)
+     so we're actually not up-to-date.  Meaningful only if it is
+     nonnegative and the modtime is actually set.  Useful only on
+     platforms with coarse clock resolution.  */
   off_t modtime_size;
 
   /* The value of text->modiff at the last auto-save.  */

diff --git a/src/fileio.c b/src/fileio.c
index a9e5975a2eb1b6bf7930c93752a781d13d12f9ec..00c04b214063c6cbd09f43bdebaf943ae5953122 100644 (file)
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -4107,8 +4107,9 @@ by calling `format-decode', which see.  */)
      restore_window_points needs the old character count.  */
   ptrdiff_t same_at_end_charpos = ZV;
 
-  /* A hint about the file size, or -1 if there is no hint.  */
-  off_t file_size_hint = -1;
+  /* The size reported by fstat, or -1 if the file was not found or its
+     size is meaningless.  */
+  off_t st_size = -1;
 
   if (current_buffer->base_buffer && ! NILP (visit))
     error ("Cannot do file visiting in an indirect buffer");
@@ -4201,11 +4202,12 @@ by calling `format-decode', which see.  */)
 
     if (regular | memory_object)
       {
-       file_size_hint = st.st_size;
+       st_size = st.st_size;
 
-       /* A negative size can happen on a platform that allows file
-          sizes greater than the maximum off_t value.  */
-       if (file_size_hint < 0)
+       /* On some ancient platforms, a regular file with a negative size means
+          the actual file size is greater than the maximum off_t value.
+          Fail now rather than doing a lot of work and exhausting memory.  */
+       if (st_size < 0)
          buffer_overflow ();
       }
 
@@ -4256,7 +4258,7 @@ by calling `format-decode', which see.  */)
      This saves a lot of needless work before a buffer overflow.
      If LIKELY_END is nonnegative, it is likely where we will stop reading.
      We could read more (or less), if the file grows (or shrinks).  */
-  off_t likely_end = min (end_offset, file_size_hint);
+  off_t likely_end = min (end_offset, st_size);
   if (beg_offset < likely_end)
     {
       ptrdiff_t buf_bytes
@@ -4303,9 +4305,7 @@ by calling `format-decode', which see.  */)
                 do not use st_size or report any SEEK_END failure.  */
              static_assert (4 * 1024 < sizeof read_buf);
              ptrdiff_t nread = emacs_full_read (fd, read_buf, 4 * 1024);
-             if (nread < 4 * 1024)
-               file_size_hint = nread;
-             else
+             if (4 * 1024 <= nread)
                {
                  off_t tailoff = emacs_fd_lseek (fd, - 3 * 1024, SEEK_END);
                  if (tailoff < 0)
@@ -4326,7 +4326,6 @@ by calling `format-decode', which see.  */)
                    }
                  else if (0 <= nread)
                    {
-                     file_size_hint = tailoff + nread;
                      nread += 1024;
                      if (4 * 1024 < nread)
                        {
@@ -4480,8 +4479,6 @@ by calling `format-decode', which see.  */)
 
          if (nread < bytes_to_read)
            {
-             file_size_hint = curpos + nread;
-
              /* Data inserted from the file match the buffer's leading bytes,
                 so there's no need to replace anything.  */
              emacs_fd_close (fd);
@@ -4521,8 +4518,6 @@ by calling `format-decode', which see.  */)
 
                  if (!giveup_match_end)
                    {
-                     file_size_hint = endpos;
-
                      /* Shrink the file's head if the file shrank to
                         be smaller than its head.  */
                      if (endpos < same_at_start_pos)
@@ -4569,7 +4564,6 @@ by calling `format-decode', which see.  */)
              if (nread < 0)
                report_file_error ("Read error", orig_filename);
              /* The file unexpectedly shrank.  */
-             file_size_hint = curpos + nread;
              giveup_match_end = true;
              break;
            }
@@ -4686,7 +4680,6 @@ by calling `format-decode', which see.  */)
 
       inserted = 0;            /* Bytes put into CONVERSION_BUFFER so far.  */
       unprocessed = 0;         /* Bytes not processed in previous loop.  */
-      file_size_hint = beg_offset;
 
       while (true)
        {
@@ -4700,7 +4693,6 @@ by calling `format-decode', which see.  */)
          if (this == 0)
            break;
 
-         file_size_hint += this;
          BUF_TEMP_SET_PT (XBUFFER (conversion_buffer),
                           BUF_Z (XBUFFER (conversion_buffer)));
          decode_coding_c_string (&coding, (unsigned char *) read_buf,
@@ -4861,7 +4853,7 @@ by calling `format-decode', which see.  */)
   /* Ensure the gap is at least one byte larger than needed for the
      estimated insertion, so that in the usual case we read
      without reallocating.  */
-  off_t inserted_estimate = min (end_offset, file_size_hint) - beg_offset;
+  off_t inserted_estimate = likely_end - beg_offset;
   if (GAP_SIZE <= inserted_estimate)
     {
       ptrdiff_t growth;
@@ -4958,8 +4950,6 @@ by calling `format-decode', which see.  */)
       }
   }
 
-  file_size_hint = beg_offset + inserted;
-
   /* Now we have either read all the file data into the gap,
      or stop reading on I/O error or quit.  If nothing was
      read, undo marking the buffer modified.  */
@@ -5119,7 +5109,7 @@ by calling `format-decode', which see.  */)
       if (NILP (handler))
        {
          current_buffer->modtime = mtime;
-         current_buffer->modtime_size = file_size_hint;
+         current_buffer->modtime_size = st_size;
          bset_filename (current_buffer, orig_filename);
        }