master b950b46f51 5/5: Fix insert-file-contents on /proc files

[Paul Eggert]

branch: master
commit b950b46f514989442fdd9937a0e96d53a3affa88
Author: Paul Eggert <eggert@cs.ucla.edu>
Commit: Paul Eggert <eggert@cs.ucla.edu>

    Fix insert-file-contents on /proc files
    
    This should fix Bug#9800 (2011-10-19).
    * src/fileio.c (Finsert_file_contents):
    Do not trust st_size even on regular files, as the file might
    be a Linux /proc file, or it might be growing.
    Instead, always read to EOF when END is nil.
---
 src/fileio.c | 57 +++++++++++++++++++++++++--------------------------------
 1 file changed, 25 insertions(+), 32 deletions(-)

diff --git a/src/fileio.c b/src/fileio.c
index ee30db8b49..b80f8d61de 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -3907,7 +3907,6 @@ by calling `format-decode', which see.  */)
   struct timespec mtime;
   int fd;
   ptrdiff_t inserted = 0;
-  ptrdiff_t how_much;
   int unprocessed;
   specpdl_ref count = SPECPDL_INDEX ();
   Lisp_Object handler, val, insval, orig_filename, old_undo;
@@ -3920,7 +3919,8 @@ by calling `format-decode', which see.  */)
   bool replace_handled = false;
   bool set_coding_system = false;
   Lisp_Object coding_system;
-  bool read_quit = false;
+  /* Negative if read error, 0 if OK so far, positive if quit.  */
+  ptrdiff_t read_quit = 0;
   /* If the undo log only contains the insertion, there's no point
      keeping it.  It's typically when we first fill a file-buffer.  */
   bool empty_undo_list_p
@@ -4404,7 +4404,7 @@ by calling `format-decode', which see.  */)
       ptrdiff_t bufpos;
       unsigned char *decoded;
       ptrdiff_t temp;
-      ptrdiff_t this = 0;
+      ptrdiff_t this;
       specpdl_ref this_count = SPECPDL_INDEX ();
       bool multibyte
        = ! NILP (BVAR (current_buffer, enable_multibyte_characters));
@@ -4580,8 +4580,12 @@ by calling `format-decode', which see.  */)
     }
 
   move_gap_both (PT, PT_BYTE);
-  if (GAP_SIZE < total)
-    make_gap (total - GAP_SIZE);
+
+  /* Ensure the gap is at least one byte larger than needed for the
+     estimated file size, so that in the usual case we read to EOF
+     without reallocating.  */
+  if (GAP_SIZE <= total)
+    make_gap (total - GAP_SIZE + 1);
 
   if (beg_offset != 0 || !NILP (replace))
     {
@@ -4589,12 +4593,6 @@ by calling `format-decode', which see.  */)
        report_file_error ("Setting file position", orig_filename);
     }
 
-  /* In the following loop, HOW_MUCH contains the total bytes read so
-     far for a regular file, and not changed for a special file.  But,
-     before exiting the loop, it is set to a negative value if I/O
-     error occurs.  */
-  how_much = 0;
-
   /* Total bytes inserted.  */
   inserted = 0;
 
@@ -4603,23 +4601,26 @@ by calling `format-decode', which see.  */)
   {
     ptrdiff_t gap_size = GAP_SIZE;
 
-    while (how_much < total)
+    while (NILP (end) || inserted < total)
       {
-       /* `try' is reserved in some compilers (Microsoft C).  */
-       ptrdiff_t trytry = min (total - how_much, READ_BUF_SIZE);
        ptrdiff_t this;
 
+       if (gap_size == 0)
+         {
+           /* The size estimate was wrong.  Make the gap 50% larger.  */
+           make_gap (GAP_SIZE >> 1);
+           gap_size = GAP_SIZE - inserted;
+         }
+
+       /* 'try' is reserved in some compilers (Microsoft C).  */
+       ptrdiff_t trytry = min (gap_size, READ_BUF_SIZE);
+       if (!NILP (end))
+         trytry = min (trytry, total - inserted);
+
        if (!seekable && NILP (end))
          {
            Lisp_Object nbytes;
 
-           /* Maybe make more room.  */
-           if (gap_size < trytry)
-             {
-               make_gap (trytry - gap_size);
-               gap_size = GAP_SIZE - inserted;
-             }
-
            /* Read from the file, capturing `quit'.  When an
               error occurs, end the loop, and arrange for a quit
               to be signaled after decoding the text we read.  */
@@ -4630,7 +4631,7 @@ by calling `format-decode', which see.  */)
 
            if (NILP (nbytes))
              {
-               read_quit = true;
+               read_quit = 1;
                break;
              }
 
@@ -4649,19 +4650,11 @@ by calling `format-decode', which see.  */)
 
        if (this <= 0)
          {
-           how_much = this;
+           read_quit = this;
            break;
          }
 
        gap_size -= this;
-
-       /* For a regular file, where TOTAL is the real size,
-          count HOW_MUCH to compare with it.
-          For a special file, where TOTAL is just a buffer size,
-          so don't bother counting in HOW_MUCH.
-          (INSERTED is where we count the number of characters inserted.)  */
-       if (seekable || !NILP (end))
-         how_much += this;
        inserted += this;
       }
   }
@@ -4682,7 +4675,7 @@ by calling `format-decode', which see.  */)
   emacs_close (fd);
   clear_unwind_protect (fd_index);
 
-  if (how_much < 0)
+  if (read_quit < 0)
     report_file_error ("Read error", orig_filename);
 
  notfound: