maint: handle file sizes more reliably

Problem reported by Samuel Thibault in <http://bugs.gnu.org/11424>.
* NEWS: Document this.
* src/dd.c (skip): Handle skipping past EOF on shared or typed
memory objects the same way as with regular files.
(dd_copy): It's OK to truncate shared memory objects.
* src/du.c (duinfo_add): Check for overflow.
(print_only_size): Report overflow.
(process_file): Ignore negative file sizes in the --apparent-size case.
* src/od.c (skip): Fix comment about st_size.
* src/split.c (main):
* src/truncate.c (do_ftruncate, main):
On files where st_size is not portable, fall back on using lseek
with SEEK_END to determine the size.  Although strictly speaking
POSIX says the behavior is implementation-defined, in practice
if lseek returns a nonnegative value it's a reasonable one to
use for the file size.
* src/system.h (usable_st_size): Symlinks have reliable st_size too.
* tests/misc/truncate-dir-fail: Don't assume that getting the size
of a dir is not allowed, as it's now allowed on many platforms,
e.g., GNU/Linux.

1 files changed, 10 insertions, 4 deletions

diff --git a/src/split.c b/src/split.c
index 062aedea9..53ee2719d 100644
--- a/src/split.c
+++ b/src/split.c
@@ -1069,7 +1069,7 @@ main (int argc, char **argv)
   static char const multipliers[] = "bEGKkMmPTYZ0";
   int c;
   int digits_optind = 0;
-  off_t file_size;
+  off_t file_size IF_LINT (= 0);
 
   initialize_main (&argc, &argv);
   set_program_name (argv[0]);
@@ -1340,12 +1340,18 @@ main (int argc, char **argv)
   if (in_blk_size == 0)
     in_blk_size = io_blksize (stat_buf);
 
-  /* stat.st_size is valid only for regular files.  For others, use 0.  */
-  file_size = S_ISREG (stat_buf.st_mode) ? stat_buf.st_size : 0;
-
   if (split_type == type_chunk_bytes || split_type == type_chunk_lines)
     {
       off_t input_offset = lseek (STDIN_FILENO, 0, SEEK_CUR);
+      if (usable_st_size (&stat_buf))
+        file_size = stat_buf.st_size;
+      else if (0 <= input_offset)
+        {
+          file_size = lseek (STDIN_FILENO, 0, SEEK_END);
+          input_offset = (file_size < 0
+                          ? file_size
+                          : lseek (STDIN_FILENO, input_offset, SEEK_SET));
+        }
       if (input_offset < 0)
         error (EXIT_FAILURE, 0, _("%s: cannot determine file size"),
                quote (infile));