libbb/xwrite: print errno on "short write" errors

Lauri Kasanen:
:: Over at TinyCore, we receive a huge number of questions of the type "I
:: got "short write", what does it mean?". Mostly for the rpi port and when
:: using bb wget.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 10 insertions, 2 deletions

diff --git a/libbb/xfuncs_printf.c b/libbb/xfuncs_printf.c
index e9222f690..1b11caf6b 100644
--- a/libbb/xfuncs_printf.c
+++ b/libbb/xfuncs_printf.c
@@ -235,8 +235,16 @@ void FAST_FUNC xwrite(int fd, const void *buf, size_t count)
 {
         if (count) {
                 ssize_t size = full_write(fd, buf, count);
-                if ((size_t)size != count)
-                        bb_error_msg_and_die("short write");
+                if ((size_t)size != count) {
+                        /*
+                         * Two cases: write error immediately;
+                         * or some writes succeeded, then we hit an error.
+                         * In either case, errno is set.
+                         */
+                        bb_perror_msg_and_die(
+                                size >= 0 ? "short write" : "write error"
+                        );
+                }
         }
 }
 void FAST_FUNC xwrite_str(int fd, const char *str)