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dd: avoid or diagnose some problems with short reads

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* src/dd.c (warn_partial_read): New static var.
(iread): Diagnose partial reads if needed.
(iwrite): Don't diagnose them here; not needed any more.
(scanargs): Determine whether partial reads should be diagnosted.
This commit is contained in:
Paul Eggert 2011-03-05 00:14:25 -08:00
parent 5bf48c1186
commit 194c1e89a4
1 changed files with 41 additions and 12 deletions
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53
src/dd.c
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@ -199,6 +199,9 @@ static int input_seek_errno;
static uintmax_t input_offset;
static bool input_offset_overflow;
/* True if a partial read should be diagnosed. */
static bool warn_partial_read;
/* Records truncated by conv=block. */
static uintmax_t r_truncate = 0;
@ -893,15 +896,36 @@ invalidate_cache (int fd, off_t len)
static ssize_t
iread (int fd, char *buf, size_t size)
{
while (true)
{
ssize_t nread;
do
{
process_signals ();
nread = read (fd, buf, size);
if (! (nread < 0 && errno == EINTR))
return nread;
}
while (nread < 0 && errno == EINTR);
if (0 < nread && warn_partial_read)
{
static ssize_t prev_nread;
if (0 < prev_nread && prev_nread < size)
{
uintmax_t prev = prev_nread;
error (0, 0, ngettext (("warning: partial read (%"PRIuMAX" byte); "
"suggest iflag=fullblock"),
("warning: partial read (%"PRIuMAX" bytes); "
"suggest iflag=fullblock"),
select_plural (prev)),
prev);
warn_partial_read = false;
}
prev_nread = nread;
}
return nread;
}
/* Wrapper around iread function to accumulate full blocks. */
@ -935,12 +959,6 @@ iwrite (int fd, char const *buf, size_t size)
{
size_t total_written = 0;
if ((output_flags & O_DIRECT) && w_partial == 1)
{
error (0, 0, _("dd: warning: partial read; oflag=direct disabled; "
"suggest iflag=fullblock"));
}
if ((output_flags & O_DIRECT) && size < output_blocksize)
{
int old_flags = fcntl (STDOUT_FILENO, F_GETFL);
@ -1175,7 +1193,7 @@ scanargs (int argc, char *const *argv)
input_blocksize = output_blocksize = blocksize;
else
{
/* POSIX says dd aggregates short reads into
/* POSIX says dd aggregates partial reads into
output_blocksize if bs= is not specified. */
conversions_mask |= C_TWOBUFS;
}
@ -1195,6 +1213,17 @@ scanargs (int argc, char *const *argv)
error (0, 0, "%s: %s", _("invalid output flag"), "'fullblock'");
usage (EXIT_FAILURE);
}
/* Warn about partial reads if bs=SIZE is given and iflag=fullblock
is not, and if counting or skipping bytes or using direct I/O.
This helps to avoid confusion with miscounts, and to avoid issues
with direct I/O on GNU/Linux. */
warn_partial_read =
(! (conversions_mask & C_TWOBUFS) && ! (input_flags & O_FULLBLOCK)
&& (skip_records
|| (0 < max_records && max_records < (uintmax_t) -1)
|| (input_flags | output_flags) & O_DIRECT));
iread_fnc = ((input_flags & O_FULLBLOCK)
? iread_fullblock
: iread);
@ -1758,7 +1787,7 @@ dd_copy (void)
There are 3 reasons why there might be unskipped blocks/bytes:
1. file is too small
2. pipe has not enough data
3. short reads */
3. partial reads */
if (us_blocks || (!input_offset_overflow && us_bytes))
{
error (0, 0,