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, 2 insertions, 1 deletions

diff --git a/src/system.h b/src/system.h
index e3d31563c..06f09cba6 100644
--- a/src/system.h
+++ b/src/system.h
@@ -605,7 +605,8 @@ bad_cast (char const *s)
 static inline bool
 usable_st_size (struct stat const *sb)
 {
-  return S_ISREG (sb->st_mode) || S_TYPEISSHM (sb) || S_TYPEISTMO (sb);
+  return (S_ISREG (sb->st_mode) || S_ISLNK (sb->st_mode)
+          || S_TYPEISSHM (sb) || S_TYPEISTMO (sb));
 }
 
 void usage (int status) ATTRIBUTE_NORETURN;