doc: clarify that `dd bs=` can immediately output short reads

* doc/coreutils.texi (dd invocation): Clarify that bs= can
cause parital reads to be immediately written to output.
* src/dd.c (usage): Hint that bs= can cause partial writes.
See http://debbugs.gnu.org/cgi/bugreport.cgi?bug=8171

diff --git a/doc/coreutils.texi b/doc/coreutils.texi
index 9f6c734..ae3712d 100644 (file)
--- a/doc/coreutils.texi
+++ b/doc/coreutils.texi
@@ -7971,8 +7971,8 @@ Set both input and output block sizes to @var{bytes}.
 This makes @command{dd} read and write @var{bytes} per block,
 overriding any @samp{ibs} and @samp{obs} settings.
 In addition, if no data-transforming @option{conv} option is specified,
-each input block is copied to the output as a single block,
-without aggregating short reads.
+input is copied to the output as soon as it's read,
+even if it is smaller than the block size.
 
 @item cbs=@var{bytes}
 @opindex cbs

diff --git a/src/dd.c b/src/dd.c
index a2b4d20..acbcea9 100644 (file)
--- a/src/dd.c
+++ b/src/dd.c
@@ -467,11 +467,11 @@ Usage: %s [OPERAND]...\n\
       fputs (_("\
 Copy a file, converting and formatting according to the operands.\n\
 \n\
-  bs=BYTES        read and write BYTES bytes at a time (also see ibs=,obs=)\n\
+  bs=BYTES        read and write up to BYTES bytes at a time\n\
   cbs=BYTES       convert BYTES bytes at a time\n\
   conv=CONVS      convert the file as per the comma separated symbol list\n\
   count=BLOCKS    copy only BLOCKS input blocks\n\
-  ibs=BYTES       read BYTES bytes at a time (default: 512)\n\
+  ibs=BYTES       read up to BYTES bytes at a time (default: 512)\n\
 "), stdout);
       fputs (_("\
   if=FILE         read from FILE instead of stdin\n\