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Subject[PATCH 3/5] Drivers: hv: fcopy: restore correct transfer length
From: Olaf Hering <>

Till recently the expected length of bytes read by the
daemon did depend on the context. It was either hv_start_fcopy or
hv_do_fcopy. The daemon had a buffer size of two pages, which was much
larger than needed.

Now the expected length of bytes read by the
daemon changed slightly. For START_FILE_COPY it is still the size of
hv_start_fcopy. But for WRITE_TO_FILE and the other operations it is as
large as the buffer that arrived via vmbus. In case of WRITE_TO_FILE
that is slightly larger than a struct hv_do_fcopy. Since the buffer in
the daemon was still larger everything was fine.

Currently, the daemon reads only what is actually needed.
The new buffer layout is as large as a struct hv_do_fcopy, for the
WRITE_TO_FILE operation. Since the kernel expects a slightly larger
size, hvt_op_read will return -EINVAL because the daemon will read
slightly less than expected. Address this by restoring the expected
buffer size in case of WRITE_TO_FILE.

Fixes: 'commit c7e490fc23eb ("Drivers: hv: fcopy: convert to hv_utils_transport")'
Fixes: 'commit 3f2baa8a7d2e ("Tools: hv: update buffer handling in hv_fcopy_daemon")'

Signed-off-by: Olaf Hering <>
Signed-off-by: K. Y. Srinivasan <>
drivers/hv/hv_fcopy.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/drivers/hv/hv_fcopy.c b/drivers/hv/hv_fcopy.c
index daa75bd41f86..2364281d8593 100644
--- a/drivers/hv/hv_fcopy.c
+++ b/drivers/hv/hv_fcopy.c
@@ -170,6 +170,10 @@ static void fcopy_send_data(struct work_struct *dummy)
out_src = smsg_out;

+ out_src = fcopy_transaction.fcopy_msg;
+ out_len = sizeof(struct hv_do_fcopy);
+ break;
out_src = fcopy_transaction.fcopy_msg;
out_len = fcopy_transaction.recv_len;
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