POSIX states about dd:
If the bs=expr operand is specified and no conversions other than
sync, noerror, or notrunc are requested, the data returned from each
input block shall be written as a separate output block; if the read
returns less than a full block and the sync conversion is not
specified, the resulting output block shall be the same size as the
input block. If the bs=expr operand is not specified, or a conversion
other than sync, noerror, or notrunc is requested, the input shall be
processed and collected into full-sized output blocks until the end of
the input is reached.
Since we aren't using conv=sync, there is no zero-padding, but our
use of bs= means that a short read results in a short write. If
instead we use ibs= and obs=, then short reads are collected and dd
only has to do a single write, which can make dd more efficient.
* src/qemu/qemu_monitor.c (qemuMonitorMigrateToFile):
Avoid 'dd bs=', since it can cause short writes.
---
src/qemu/qemu_monitor.c | 3 ++-
1 files changed, 2 insertions(+), 1 deletions(-)
diff --git a/src/qemu/qemu_monitor.c b/src/qemu/qemu_monitor.c
index eb6f8d4..765a1ae 100644
--- a/src/qemu/qemu_monitor.c
+++ b/src/qemu/qemu_monitor.c
@@ -1499,10 +1499,11 @@ int qemuMonitorMigrateToFile(qemuMonitorPtr mon,
* <> redirection to avoid truncating a regular file. */
if (virAsprintf(&dest, "exec:" VIR_WRAPPER_SHELL_PREFIX "%s | "
"{ dd bs=%llu seek=%llu if=/dev/null && "
- "dd bs=%llu; } 1<>%s" VIR_WRAPPER_SHELL_SUFFIX,
+ "dd ibs=%llu obs=%llu; } 1<>%s" VIR_WRAPPER_SHELL_SUFFIX,
argstr, QEMU_MONITOR_MIGRATE_TO_FILE_BS,
offset / QEMU_MONITOR_MIGRATE_TO_FILE_BS,
QEMU_MONITOR_MIGRATE_TO_FILE_TRANSFER_SIZE,
+ QEMU_MONITOR_MIGRATE_TO_FILE_TRANSFER_SIZE,
safe_target) < 0) {
virReportOOMError();
goto cleanup;
--
1.7.4
--
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