include/io/channel.h | 1 + io/channel-socket.c | 12 ++++++++---- io/channel.c | 2 +- migration/qemu-file.c | 3 ++- 4 files changed, 12 insertions(+), 6 deletions(-)
In migration we want to pass fd "as is", not changing its
blocking status.
The only current user of these fds is CPR state (through VMSTATE_FD),
which of-course doesn't want to modify fds on target when source is
still running and use these fds.
Suggested-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
---
v3: RESEND, add qemu-devel to CC, sorry for the noise
v2: rework, following Daniel's suggestion to use flag.
include/io/channel.h | 1 +
io/channel-socket.c | 12 ++++++++----
io/channel.c | 2 +-
migration/qemu-file.c | 3 ++-
4 files changed, 12 insertions(+), 6 deletions(-)
diff --git a/include/io/channel.h b/include/io/channel.h
index 234e5db70d..5394f50768 100644
--- a/include/io/channel.h
+++ b/include/io/channel.h
@@ -36,6 +36,7 @@ OBJECT_DECLARE_TYPE(QIOChannel, QIOChannelClass,
#define QIO_CHANNEL_READ_FLAG_MSG_PEEK 0x1
#define QIO_CHANNEL_READ_FLAG_RELAXED_EOF 0x2
+#define QIO_CHANNEL_READ_FLAG_PRESERVE_BLOCKING 0x4
typedef enum QIOChannelFeature QIOChannelFeature;
diff --git a/io/channel-socket.c b/io/channel-socket.c
index 3b7ca924ff..2f6e2d84a3 100644
--- a/io/channel-socket.c
+++ b/io/channel-socket.c
@@ -464,7 +464,8 @@ static void qio_channel_socket_finalize(Object *obj)
#ifndef WIN32
static void qio_channel_socket_copy_fds(struct msghdr *msg,
- int **fds, size_t *nfds)
+ int **fds, size_t *nfds,
+ bool preserve_blocking)
{
struct cmsghdr *cmsg;
@@ -497,8 +498,10 @@ static void qio_channel_socket_copy_fds(struct msghdr *msg,
continue;
}
- /* O_NONBLOCK is preserved across SCM_RIGHTS so reset it */
- qemu_socket_set_block(fd);
+ if (!preserve_blocking) {
+ /* O_NONBLOCK is preserved across SCM_RIGHTS so reset it */
+ qemu_socket_set_block(fd);
+ }
#ifndef MSG_CMSG_CLOEXEC
qemu_set_cloexec(fd);
@@ -556,7 +559,8 @@ static ssize_t qio_channel_socket_readv(QIOChannel *ioc,
}
if (fds && nfds) {
- qio_channel_socket_copy_fds(&msg, fds, nfds);
+ qio_channel_socket_copy_fds(
+ &msg, fds, nfds, flags & QIO_CHANNEL_READ_FLAG_PRESERVE_BLOCKING);
}
return ret;
diff --git a/io/channel.c b/io/channel.c
index ebd9322765..50d5f7b10b 100644
--- a/io/channel.c
+++ b/io/channel.c
@@ -58,7 +58,7 @@ ssize_t qio_channel_readv_full(QIOChannel *ioc,
{
QIOChannelClass *klass = QIO_CHANNEL_GET_CLASS(ioc);
- if ((fds || nfds) &&
+ if ((fds || nfds || (flags & QIO_CHANNEL_READ_FLAG_PRESERVE_BLOCKING)) &&
!qio_channel_has_feature(ioc, QIO_CHANNEL_FEATURE_FD_PASS)) {
error_setg_errno(errp, EINVAL,
"Channel does not support file descriptor passing");
diff --git a/migration/qemu-file.c b/migration/qemu-file.c
index b6ac190034..92c7b5678b 100644
--- a/migration/qemu-file.c
+++ b/migration/qemu-file.c
@@ -324,6 +324,7 @@ static ssize_t coroutine_mixed_fn qemu_fill_buffer(QEMUFile *f)
size_t nfd = 0;
int **pfds = f->can_pass_fd ? &fds : NULL;
size_t *pnfd = f->can_pass_fd ? &nfd : NULL;
+ int flags = f->can_pass_fd ? QIO_CHANNEL_READ_FLAG_PRESERVE_BLOCKING : 0;
assert(!qemu_file_is_writable(f));
@@ -340,7 +341,7 @@ static ssize_t coroutine_mixed_fn qemu_fill_buffer(QEMUFile *f)
do {
struct iovec iov = { f->buf + pending, IO_BUF_SIZE - pending };
- len = qio_channel_readv_full(f->ioc, &iov, 1, pfds, pnfd, 0,
+ len = qio_channel_readv_full(f->ioc, &iov, 1, pfds, pnfd, flags,
&local_error);
if (len == QIO_CHANNEL_ERR_BLOCK) {
if (qemu_in_coroutine()) {
--
2.48.1
On Wed, Sep 10, 2025 at 05:31:56PM +0300, Vladimir Sementsov-Ogievskiy wrote:
> In migration we want to pass fd "as is", not changing its
> blocking status.
>
> The only current user of these fds is CPR state (through VMSTATE_FD),
> which of-course doesn't want to modify fds on target when source is
> still running and use these fds.
>
> Suggested-by: Daniel P. Berrangé <berrange@redhat.com>
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
> ---
>
> v3: RESEND, add qemu-devel to CC, sorry for the noise
> v2: rework, following Daniel's suggestion to use flag.
>
> include/io/channel.h | 1 +
> io/channel-socket.c | 12 ++++++++----
> io/channel.c | 2 +-
> migration/qemu-file.c | 3 ++-
> 4 files changed, 12 insertions(+), 6 deletions(-)
>
> diff --git a/include/io/channel.h b/include/io/channel.h
> index 234e5db70d..5394f50768 100644
> --- a/include/io/channel.h
> +++ b/include/io/channel.h
> @@ -36,6 +36,7 @@ OBJECT_DECLARE_TYPE(QIOChannel, QIOChannelClass,
>
> #define QIO_CHANNEL_READ_FLAG_MSG_PEEK 0x1
> #define QIO_CHANNEL_READ_FLAG_RELAXED_EOF 0x2
> +#define QIO_CHANNEL_READ_FLAG_PRESERVE_BLOCKING 0x4
Shouldn't the name reflect FD somehow? Or it can imply preservation
blocking for the channel itself.
QIO_CHANNEL_READ_FLAG_FD_PRESERVE_BLOCKING
QIO_CHANNEL_READ_FLAG_PRESERVE_FD_BLOCKING
...
>
> typedef enum QIOChannelFeature QIOChannelFeature;
>
> diff --git a/io/channel-socket.c b/io/channel-socket.c
> index 3b7ca924ff..2f6e2d84a3 100644
> --- a/io/channel-socket.c
> +++ b/io/channel-socket.c
> @@ -464,7 +464,8 @@ static void qio_channel_socket_finalize(Object *obj)
>
> #ifndef WIN32
> static void qio_channel_socket_copy_fds(struct msghdr *msg,
> - int **fds, size_t *nfds)
> + int **fds, size_t *nfds,
> + bool preserve_blocking)
> {
> struct cmsghdr *cmsg;
>
> @@ -497,8 +498,10 @@ static void qio_channel_socket_copy_fds(struct msghdr *msg,
> continue;
> }
>
> - /* O_NONBLOCK is preserved across SCM_RIGHTS so reset it */
> - qemu_socket_set_block(fd);
> + if (!preserve_blocking) {
> + /* O_NONBLOCK is preserved across SCM_RIGHTS so reset it */
> + qemu_socket_set_block(fd);
> + }
>
> #ifndef MSG_CMSG_CLOEXEC
> qemu_set_cloexec(fd);
> @@ -556,7 +559,8 @@ static ssize_t qio_channel_socket_readv(QIOChannel *ioc,
> }
>
> if (fds && nfds) {
> - qio_channel_socket_copy_fds(&msg, fds, nfds);
> + qio_channel_socket_copy_fds(
> + &msg, fds, nfds, flags & QIO_CHANNEL_READ_FLAG_PRESERVE_BLOCKING);
> }
>
> return ret;
> diff --git a/io/channel.c b/io/channel.c
> index ebd9322765..50d5f7b10b 100644
> --- a/io/channel.c
> +++ b/io/channel.c
> @@ -58,7 +58,7 @@ ssize_t qio_channel_readv_full(QIOChannel *ioc,
> {
> QIOChannelClass *klass = QIO_CHANNEL_GET_CLASS(ioc);
>
> - if ((fds || nfds) &&
> + if ((fds || nfds || (flags & QIO_CHANNEL_READ_FLAG_PRESERVE_BLOCKING)) &&
Not a huge deal, but.. IMHO we can simply ignore this flag when fds==NULL.
It can also make callers' lives slightly easier too by always passing in
this flag when necessary, like in below.
> !qio_channel_has_feature(ioc, QIO_CHANNEL_FEATURE_FD_PASS)) {
> error_setg_errno(errp, EINVAL,
> "Channel does not support file descriptor passing");
> diff --git a/migration/qemu-file.c b/migration/qemu-file.c
> index b6ac190034..92c7b5678b 100644
> --- a/migration/qemu-file.c
> +++ b/migration/qemu-file.c
> @@ -324,6 +324,7 @@ static ssize_t coroutine_mixed_fn qemu_fill_buffer(QEMUFile *f)
> size_t nfd = 0;
> int **pfds = f->can_pass_fd ? &fds : NULL;
> size_t *pnfd = f->can_pass_fd ? &nfd : NULL;
> + int flags = f->can_pass_fd ? QIO_CHANNEL_READ_FLAG_PRESERVE_BLOCKING : 0;
>
> assert(!qemu_file_is_writable(f));
>
> @@ -340,7 +341,7 @@ static ssize_t coroutine_mixed_fn qemu_fill_buffer(QEMUFile *f)
>
> do {
> struct iovec iov = { f->buf + pending, IO_BUF_SIZE - pending };
> - len = qio_channel_readv_full(f->ioc, &iov, 1, pfds, pnfd, 0,
> + len = qio_channel_readv_full(f->ioc, &iov, 1, pfds, pnfd, flags,
> &local_error);
> if (len == QIO_CHANNEL_ERR_BLOCK) {
> if (qemu_in_coroutine()) {
> --
> 2.48.1
>
--
Peter Xu
On 10.09.25 19:47, Peter Xu wrote:
> On Wed, Sep 10, 2025 at 05:31:56PM +0300, Vladimir Sementsov-Ogievskiy wrote:
>> In migration we want to pass fd "as is", not changing its
>> blocking status.
>>
>> The only current user of these fds is CPR state (through VMSTATE_FD),
>> which of-course doesn't want to modify fds on target when source is
>> still running and use these fds.
>>
>> Suggested-by: Daniel P. Berrangé <berrange@redhat.com>
>> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
>> ---
>>
>> v3: RESEND, add qemu-devel to CC, sorry for the noise
>> v2: rework, following Daniel's suggestion to use flag.
>>
>> include/io/channel.h | 1 +
>> io/channel-socket.c | 12 ++++++++----
>> io/channel.c | 2 +-
>> migration/qemu-file.c | 3 ++-
>> 4 files changed, 12 insertions(+), 6 deletions(-)
>>
>> diff --git a/include/io/channel.h b/include/io/channel.h
>> index 234e5db70d..5394f50768 100644
>> --- a/include/io/channel.h
>> +++ b/include/io/channel.h
>> @@ -36,6 +36,7 @@ OBJECT_DECLARE_TYPE(QIOChannel, QIOChannelClass,
>>
>> #define QIO_CHANNEL_READ_FLAG_MSG_PEEK 0x1
>> #define QIO_CHANNEL_READ_FLAG_RELAXED_EOF 0x2
>> +#define QIO_CHANNEL_READ_FLAG_PRESERVE_BLOCKING 0x4
>
> Shouldn't the name reflect FD somehow? Or it can imply preservation
> blocking for the channel itself.
>
> QIO_CHANNEL_READ_FLAG_FD_PRESERVE_BLOCKING
> QIO_CHANNEL_READ_FLAG_PRESERVE_FD_BLOCKING
> ...
>
>>
>> typedef enum QIOChannelFeature QIOChannelFeature;
>>
>> diff --git a/io/channel-socket.c b/io/channel-socket.c
>> index 3b7ca924ff..2f6e2d84a3 100644
>> --- a/io/channel-socket.c
>> +++ b/io/channel-socket.c
>> @@ -464,7 +464,8 @@ static void qio_channel_socket_finalize(Object *obj)
>>
>> #ifndef WIN32
>> static void qio_channel_socket_copy_fds(struct msghdr *msg,
>> - int **fds, size_t *nfds)
>> + int **fds, size_t *nfds,
>> + bool preserve_blocking)
>> {
>> struct cmsghdr *cmsg;
>>
>> @@ -497,8 +498,10 @@ static void qio_channel_socket_copy_fds(struct msghdr *msg,
>> continue;
>> }
>>
>> - /* O_NONBLOCK is preserved across SCM_RIGHTS so reset it */
>> - qemu_socket_set_block(fd);
>> + if (!preserve_blocking) {
>> + /* O_NONBLOCK is preserved across SCM_RIGHTS so reset it */
>> + qemu_socket_set_block(fd);
>> + }
>>
>> #ifndef MSG_CMSG_CLOEXEC
>> qemu_set_cloexec(fd);
>> @@ -556,7 +559,8 @@ static ssize_t qio_channel_socket_readv(QIOChannel *ioc,
>> }
>>
>> if (fds && nfds) {
>> - qio_channel_socket_copy_fds(&msg, fds, nfds);
>> + qio_channel_socket_copy_fds(
>> + &msg, fds, nfds, flags & QIO_CHANNEL_READ_FLAG_PRESERVE_BLOCKING);
>> }
>>
>> return ret;
>> diff --git a/io/channel.c b/io/channel.c
>> index ebd9322765..50d5f7b10b 100644
>> --- a/io/channel.c
>> +++ b/io/channel.c
>> @@ -58,7 +58,7 @@ ssize_t qio_channel_readv_full(QIOChannel *ioc,
>> {
>> QIOChannelClass *klass = QIO_CHANNEL_GET_CLASS(ioc);
>>
>> - if ((fds || nfds) &&
>> + if ((fds || nfds || (flags & QIO_CHANNEL_READ_FLAG_PRESERVE_BLOCKING)) &&
>
> Not a huge deal, but.. IMHO we can simply ignore this flag when fds==NULL.
>
> It can also make callers' lives slightly easier too by always passing in
> this flag when necessary, like in below.
>
>> !qio_channel_has_feature(ioc, QIO_CHANNEL_FEATURE_FD_PASS)) {
>> error_setg_errno(errp, EINVAL,
>> "Channel does not support file descriptor passing");
>> diff --git a/migration/qemu-file.c b/migration/qemu-file.c
>> index b6ac190034..92c7b5678b 100644
>> --- a/migration/qemu-file.c
>> +++ b/migration/qemu-file.c
>> @@ -324,6 +324,7 @@ static ssize_t coroutine_mixed_fn qemu_fill_buffer(QEMUFile *f)
>> size_t nfd = 0;
>> int **pfds = f->can_pass_fd ? &fds : NULL;
>> size_t *pnfd = f->can_pass_fd ? &nfd : NULL;
>> + int flags = f->can_pass_fd ? QIO_CHANNEL_READ_FLAG_PRESERVE_BLOCKING : 0;
>>
>> assert(!qemu_file_is_writable(f));
>>
>> @@ -340,7 +341,7 @@ static ssize_t coroutine_mixed_fn qemu_fill_buffer(QEMUFile *f)
>>
>> do {
>> struct iovec iov = { f->buf + pending, IO_BUF_SIZE - pending };
>> - len = qio_channel_readv_full(f->ioc, &iov, 1, pfds, pnfd, 0,
>> + len = qio_channel_readv_full(f->ioc, &iov, 1, pfds, pnfd, flags,
>> &local_error);
>> if (len == QIO_CHANNEL_ERR_BLOCK) {
>> if (qemu_in_coroutine()) {
>> --
>> 2.48.1
>>
>
I'm OK with both changes, can resend. Daniel, are you?
--
Best regards,
Vladimir
On Wed, Sep 10, 2025 at 05:31:56PM +0300, Vladimir Sementsov-Ogievskiy wrote: > In migration we want to pass fd "as is", not changing its > blocking status. > > The only current user of these fds is CPR state (through VMSTATE_FD), > which of-course doesn't want to modify fds on target when source is > still running and use these fds. > > Suggested-by: Daniel P. Berrangé <berrange@redhat.com> > Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru> Reviewed-by: Daniel P. Berrangé <berrange@redhat.com> With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
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