[Qemu-devel] [RFC PATCH 0/2] Migration: support working on file:url

[Qemu-devel] [RFC PATCH 0/2] Migration: support working on file:url

[zhanghailiang]

It is more simple to use file:url to migrate VM into file.
Besides, it will be used in memory snapshot.

Test:
1) migrate VM state into file:
   migrate file:url
2) Restore VM from the file:
   qemu-system-x86_64 xxx  --incoming file:url

zhanghailiang (2):
  migration: Allow the migrate command to work on file:urls
  migration: Allow -incoming to work on file: urls

 include/migration/migration.h |  4 +++
 migration/fd.c                | 71 +++++++++++++++++++++++++++++++++++--------
 migration/migration.c         |  4 +++
 migration/trace-events        |  2 ++
 4 files changed, 69 insertions(+), 12 deletions(-)

-- 
1.8.3.1

[Qemu-devel] [RFC PATCH 1/2] migration: Allow the migrate command to work on file:urls

[zhanghailiang]

Usage:
(qemu) migrate file:/path/to/vm_statefile

Signed-off-by: zhanghailiang <zhang.zhanghailiang@huawei.com>
Signed-off-by: Benoit Canet <benoit.canet@gmail.com>
---
 include/migration/migration.h |  2 ++
 migration/fd.c                | 34 ++++++++++++++++++++++++++++------
 migration/migration.c         |  2 ++
 migration/trace-events        |  1 +
 4 files changed, 33 insertions(+), 6 deletions(-)

diff --git a/include/migration/migration.h b/include/migration/migration.h
index 3c96623..cc2e4f6 100644
--- a/include/migration/migration.h
+++ b/include/migration/migration.h
@@ -221,6 +221,8 @@ void fd_start_incoming_migration(const char *path, Error **errp);
 
 void fd_start_outgoing_migration(MigrationState *s, const char *fdname, Error **errp);
 
+void file_start_outgoing_migration(MigrationState *s, const char *filename, Error **errp);
+
 void rdma_start_outgoing_migration(void *opaque, const char *host_port, Error **errp);
 
 void rdma_start_incoming_migration(const char *host_port, Error **errp);
diff --git a/migration/fd.c b/migration/fd.c
index 84a10fd..fa5df67 100644
--- a/migration/fd.c
+++ b/migration/fd.c
@@ -23,15 +23,11 @@
 #include "trace.h"
 
 
-void fd_start_outgoing_migration(MigrationState *s, const char *fdname, Error **errp)
+static void fd_start_outgoing_migration_core(MigrationState *s, int fd,
+                                             Error **errp)
 {
     QIOChannel *ioc;
-    int fd = monitor_get_fd(cur_mon, fdname, errp);
-    if (fd == -1) {
-        return;
-    }
 
-    trace_migration_fd_outgoing(fd);
     ioc = qio_channel_new_fd(fd, errp);
     if (!ioc) {
         close(fd);
@@ -42,6 +38,32 @@ void fd_start_outgoing_migration(MigrationState *s, const char *fdname, Error **
     object_unref(OBJECT(ioc));
 }
 
+void fd_start_outgoing_migration(MigrationState *s, const char *fdname, Error **errp)
+{
+    int fd = monitor_get_fd(cur_mon, fdname, errp);
+    if (fd == -1) {
+        return;
+    }
+
+    trace_migration_fd_outgoing(fd);
+    fd_start_outgoing_migration_core(s, fd, errp);
+}
+
+void file_start_outgoing_migration(MigrationState *s, const char *filename,
+                                   Error **errp)
+{
+    int fd;
+
+    fd = qemu_open(filename, O_CREAT | O_TRUNC | O_WRONLY, S_IRUSR | S_IWUSR);
+    if (fd < 0) {
+        error_setg_errno(errp, errno, "Failed to open file: %s", filename);
+        return;
+    }
+    
+    trace_migration_file_outgoing(filename);
+    fd_start_outgoing_migration_core(s, fd, errp);
+}
+
 static gboolean fd_accept_incoming_migration(QIOChannel *ioc,
                                              GIOCondition condition,
                                              gpointer opaque)
diff --git a/migration/migration.c b/migration/migration.c
index c4e0193..097adba 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -1109,6 +1109,8 @@ void qmp_migrate(const char *uri, bool has_blk, bool blk,
         unix_start_outgoing_migration(s, p, &local_err);
     } else if (strstart(uri, "fd:", &p)) {
         fd_start_outgoing_migration(s, p, &local_err);
+    } else if (strstart(uri, "file:", &p)) {
+        file_start_outgoing_migration(s, p, &local_err);
     } else {
         error_setg(errp, QERR_INVALID_PARAMETER_VALUE, "uri",
                    "a valid migration protocol");
diff --git a/migration/trace-events b/migration/trace-events
index 8568dab..4fca64c 100644
--- a/migration/trace-events
+++ b/migration/trace-events
@@ -194,6 +194,7 @@ migration_exec_incoming(const char *cmd) "cmd=%s"
 # migration/fd.c
 migration_fd_outgoing(int fd) "fd=%d"
 migration_fd_incoming(int fd) "fd=%d"
+migration_file_outgoing(const char *filename) "file=%s"
 
 # migration/socket.c
 migration_socket_incoming_accepted(void) ""
-- 
1.8.3.1

[Qemu-devel] [RFC PATCH 2/2] migration: Allow -incoming to work on file: urls

[zhanghailiang]

Usage:
-incoming file:/path/to/vm_statefile

Besides, use qemu_strtol() instead of strtol().

Signed-off-by: zhanghailiang <zhang.zhanghailiang@huawei.com>
Signed-off-by: Benoit Canet <benoit.canet@gmail.com>
---
 include/migration/migration.h |  2 ++
 migration/fd.c                | 37 +++++++++++++++++++++++++++++++------
 migration/migration.c         |  2 ++
 migration/trace-events        |  1 +
 4 files changed, 36 insertions(+), 6 deletions(-)

diff --git a/include/migration/migration.h b/include/migration/migration.h
index cc2e4f6..a7f1051 100644
--- a/include/migration/migration.h
+++ b/include/migration/migration.h
@@ -223,6 +223,8 @@ void fd_start_outgoing_migration(MigrationState *s, const char *fdname, Error **
 
 void file_start_outgoing_migration(MigrationState *s, const char *filename, Error **errp);
 
+void file_start_incoming_migration(const char *filename, Error **errp);
+
 void rdma_start_outgoing_migration(void *opaque, const char *host_port, Error **errp);
 
 void rdma_start_incoming_migration(const char *host_port, Error **errp);
diff --git a/migration/fd.c b/migration/fd.c
index fa5df67..472876c 100644
--- a/migration/fd.c
+++ b/migration/fd.c
@@ -21,7 +21,7 @@
 #include "monitor/monitor.h"
 #include "io/channel-util.h"
 #include "trace.h"
-
+#include "qemu/cutils.h"
 
 static void fd_start_outgoing_migration_core(MigrationState *s, int fd,
                                              Error **errp)
@@ -73,13 +73,9 @@ static gboolean fd_accept_incoming_migration(QIOChannel *ioc,
     return FALSE; /* unregister */
 }
 
-void fd_start_incoming_migration(const char *infd, Error **errp)
+static void fd_start_incoming_migration_core(int fd, Error **errp)
 {
     QIOChannel *ioc;
-    int fd;
-
-    fd = strtol(infd, NULL, 0);
-    trace_migration_fd_incoming(fd);
 
     ioc = qio_channel_new_fd(fd, errp);
     if (!ioc) {
@@ -93,3 +89,32 @@ void fd_start_incoming_migration(const char *infd, Error **errp)
                           NULL,
                           NULL);
 }
+
+void fd_start_incoming_migration(const char *infd, Error **errp)
+{
+    long fd;
+    int err;
+
+    err = qemu_strtol(infd, NULL, 0, &fd);
+    if (err < 0) {
+        error_setg_errno(errp, -err, "Failed to convert string '%s'"
+                        " to number", infd);
+        return;
+    }
+
+    trace_migration_fd_incoming((int)fd);
+    fd_start_incoming_migration_core((int)fd, errp);
+}
+
+void file_start_incoming_migration(const char *filename, Error **errp)
+{
+    int fd;
+
+    fd = qemu_open(filename, O_RDONLY);
+    if (fd < 0) {
+        error_setg_errno(errp, errno, "Failed to open file:%s", filename);
+        return;
+    }
+    trace_migration_file_incoming(filename);
+    fd_start_incoming_migration_core(fd, errp);
+}
diff --git a/migration/migration.c b/migration/migration.c
index 097adba..5ed3fea 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -315,6 +315,8 @@ void qemu_start_incoming_migration(const char *uri, Error **errp)
         unix_start_incoming_migration(p, errp);
     } else if (strstart(uri, "fd:", &p)) {
         fd_start_incoming_migration(p, errp);
+    } else if (strstart(uri, "file:", &p)) {
+        file_start_incoming_migration(p, errp);
     } else {
         error_setg(errp, "unknown migration protocol: %s", uri);
     }
diff --git a/migration/trace-events b/migration/trace-events
index 4fca64c..8a76595 100644
--- a/migration/trace-events
+++ b/migration/trace-events
@@ -195,6 +195,7 @@ migration_exec_incoming(const char *cmd) "cmd=%s"
 migration_fd_outgoing(int fd) "fd=%d"
 migration_fd_incoming(int fd) "fd=%d"
 migration_file_outgoing(const char *filename) "file=%s"
+migration_file_incoming(const char *filename) "file=%s"
 
 # migration/socket.c
 migration_socket_incoming_accepted(void) ""
-- 
1.8.3.1

Re: [Qemu-devel] [RFC PATCH 1/2] migration: Allow the migrate command to work on file:urls

[Dr. David Alan Gilbert]

* zhanghailiang (zhang.zhanghailiang@huawei.com) wrote:
> Usage:
> (qemu) migrate file:/path/to/vm_statefile
> 
> Signed-off-by: zhanghailiang <zhang.zhanghailiang@huawei.com>
> Signed-off-by: Benoit Canet <benoit.canet@gmail.com>

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

> ---
>  include/migration/migration.h |  2 ++
>  migration/fd.c                | 34 ++++++++++++++++++++++++++++------
>  migration/migration.c         |  2 ++
>  migration/trace-events        |  1 +
>  4 files changed, 33 insertions(+), 6 deletions(-)
> 
> diff --git a/include/migration/migration.h b/include/migration/migration.h
> index 3c96623..cc2e4f6 100644
> --- a/include/migration/migration.h
> +++ b/include/migration/migration.h
> @@ -221,6 +221,8 @@ void fd_start_incoming_migration(const char *path, Error **errp);
>  
>  void fd_start_outgoing_migration(MigrationState *s, const char *fdname, Error **errp);
>  
> +void file_start_outgoing_migration(MigrationState *s, const char *filename, Error **errp);
> +
>  void rdma_start_outgoing_migration(void *opaque, const char *host_port, Error **errp);
>  
>  void rdma_start_incoming_migration(const char *host_port, Error **errp);
> diff --git a/migration/fd.c b/migration/fd.c
> index 84a10fd..fa5df67 100644
> --- a/migration/fd.c
> +++ b/migration/fd.c
> @@ -23,15 +23,11 @@
>  #include "trace.h"
>  
>  
> -void fd_start_outgoing_migration(MigrationState *s, const char *fdname, Error **errp)
> +static void fd_start_outgoing_migration_core(MigrationState *s, int fd,
> +                                             Error **errp)
>  {
>      QIOChannel *ioc;
> -    int fd = monitor_get_fd(cur_mon, fdname, errp);
> -    if (fd == -1) {
> -        return;
> -    }
>  
> -    trace_migration_fd_outgoing(fd);
>      ioc = qio_channel_new_fd(fd, errp);
>      if (!ioc) {
>          close(fd);
> @@ -42,6 +38,32 @@ void fd_start_outgoing_migration(MigrationState *s, const char *fdname, Error **
>      object_unref(OBJECT(ioc));
>  }
>  
> +void fd_start_outgoing_migration(MigrationState *s, const char *fdname, Error **errp)
> +{
> +    int fd = monitor_get_fd(cur_mon, fdname, errp);
> +    if (fd == -1) {
> +        return;
> +    }
> +
> +    trace_migration_fd_outgoing(fd);
> +    fd_start_outgoing_migration_core(s, fd, errp);
> +}
> +
> +void file_start_outgoing_migration(MigrationState *s, const char *filename,
> +                                   Error **errp)
> +{
> +    int fd;
> +
> +    fd = qemu_open(filename, O_CREAT | O_TRUNC | O_WRONLY, S_IRUSR | S_IWUSR);
> +    if (fd < 0) {
> +        error_setg_errno(errp, errno, "Failed to open file: %s", filename);
> +        return;
> +    }
> +    
> +    trace_migration_file_outgoing(filename);
> +    fd_start_outgoing_migration_core(s, fd, errp);
> +}
> +
>  static gboolean fd_accept_incoming_migration(QIOChannel *ioc,
>                                               GIOCondition condition,
>                                               gpointer opaque)
> diff --git a/migration/migration.c b/migration/migration.c
> index c4e0193..097adba 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -1109,6 +1109,8 @@ void qmp_migrate(const char *uri, bool has_blk, bool blk,
>          unix_start_outgoing_migration(s, p, &local_err);
>      } else if (strstart(uri, "fd:", &p)) {
>          fd_start_outgoing_migration(s, p, &local_err);
> +    } else if (strstart(uri, "file:", &p)) {
> +        file_start_outgoing_migration(s, p, &local_err);
>      } else {
>          error_setg(errp, QERR_INVALID_PARAMETER_VALUE, "uri",
>                     "a valid migration protocol");
> diff --git a/migration/trace-events b/migration/trace-events
> index 8568dab..4fca64c 100644
> --- a/migration/trace-events
> +++ b/migration/trace-events
> @@ -194,6 +194,7 @@ migration_exec_incoming(const char *cmd) "cmd=%s"
>  # migration/fd.c
>  migration_fd_outgoing(int fd) "fd=%d"
>  migration_fd_incoming(int fd) "fd=%d"
> +migration_file_outgoing(const char *filename) "file=%s"
>  
>  # migration/socket.c
>  migration_socket_incoming_accepted(void) ""
> -- 
> 1.8.3.1
> 
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK

Re: [Qemu-devel] [RFC PATCH 2/2] migration: Allow -incoming to work on file: urls

[Dr. David Alan Gilbert]

* zhanghailiang (zhang.zhanghailiang@huawei.com) wrote:
> Usage:
> -incoming file:/path/to/vm_statefile
> 
> Besides, use qemu_strtol() instead of strtol().
> 
> Signed-off-by: zhanghailiang <zhang.zhanghailiang@huawei.com>
> Signed-off-by: Benoit Canet <benoit.canet@gmail.com>

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

> ---
>  include/migration/migration.h |  2 ++
>  migration/fd.c                | 37 +++++++++++++++++++++++++++++++------
>  migration/migration.c         |  2 ++
>  migration/trace-events        |  1 +
>  4 files changed, 36 insertions(+), 6 deletions(-)
> 
> diff --git a/include/migration/migration.h b/include/migration/migration.h
> index cc2e4f6..a7f1051 100644
> --- a/include/migration/migration.h
> +++ b/include/migration/migration.h
> @@ -223,6 +223,8 @@ void fd_start_outgoing_migration(MigrationState *s, const char *fdname, Error **
>  
>  void file_start_outgoing_migration(MigrationState *s, const char *filename, Error **errp);
>  
> +void file_start_incoming_migration(const char *filename, Error **errp);
> +
>  void rdma_start_outgoing_migration(void *opaque, const char *host_port, Error **errp);
>  
>  void rdma_start_incoming_migration(const char *host_port, Error **errp);
> diff --git a/migration/fd.c b/migration/fd.c
> index fa5df67..472876c 100644
> --- a/migration/fd.c
> +++ b/migration/fd.c
> @@ -21,7 +21,7 @@
>  #include "monitor/monitor.h"
>  #include "io/channel-util.h"
>  #include "trace.h"
> -
> +#include "qemu/cutils.h"
>  
>  static void fd_start_outgoing_migration_core(MigrationState *s, int fd,
>                                               Error **errp)
> @@ -73,13 +73,9 @@ static gboolean fd_accept_incoming_migration(QIOChannel *ioc,
>      return FALSE; /* unregister */
>  }
>  
> -void fd_start_incoming_migration(const char *infd, Error **errp)
> +static void fd_start_incoming_migration_core(int fd, Error **errp)
>  {
>      QIOChannel *ioc;
> -    int fd;
> -
> -    fd = strtol(infd, NULL, 0);
> -    trace_migration_fd_incoming(fd);
>  
>      ioc = qio_channel_new_fd(fd, errp);
>      if (!ioc) {
> @@ -93,3 +89,32 @@ void fd_start_incoming_migration(const char *infd, Error **errp)
>                            NULL,
>                            NULL);
>  }
> +
> +void fd_start_incoming_migration(const char *infd, Error **errp)
> +{
> +    long fd;
> +    int err;
> +
> +    err = qemu_strtol(infd, NULL, 0, &fd);
> +    if (err < 0) {
> +        error_setg_errno(errp, -err, "Failed to convert string '%s'"
> +                        " to number", infd);
> +        return;
> +    }
> +
> +    trace_migration_fd_incoming((int)fd);
> +    fd_start_incoming_migration_core((int)fd, errp);
> +}
> +
> +void file_start_incoming_migration(const char *filename, Error **errp)
> +{
> +    int fd;
> +
> +    fd = qemu_open(filename, O_RDONLY);
> +    if (fd < 0) {
> +        error_setg_errno(errp, errno, "Failed to open file:%s", filename);
> +        return;
> +    }
> +    trace_migration_file_incoming(filename);
> +    fd_start_incoming_migration_core(fd, errp);
> +}
> diff --git a/migration/migration.c b/migration/migration.c
> index 097adba..5ed3fea 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -315,6 +315,8 @@ void qemu_start_incoming_migration(const char *uri, Error **errp)
>          unix_start_incoming_migration(p, errp);
>      } else if (strstart(uri, "fd:", &p)) {
>          fd_start_incoming_migration(p, errp);
> +    } else if (strstart(uri, "file:", &p)) {
> +        file_start_incoming_migration(p, errp);
>      } else {
>          error_setg(errp, "unknown migration protocol: %s", uri);
>      }
> diff --git a/migration/trace-events b/migration/trace-events
> index 4fca64c..8a76595 100644
> --- a/migration/trace-events
> +++ b/migration/trace-events
> @@ -195,6 +195,7 @@ migration_exec_incoming(const char *cmd) "cmd=%s"
>  migration_fd_outgoing(int fd) "fd=%d"
>  migration_fd_incoming(int fd) "fd=%d"
>  migration_file_outgoing(const char *filename) "file=%s"
> +migration_file_incoming(const char *filename) "file=%s"
>  
>  # migration/socket.c
>  migration_socket_incoming_accepted(void) ""
> -- 
> 1.8.3.1
> 
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK

Re: [Qemu-devel] [RFC PATCH 1/2] migration: Allow the migrate command to work on file:urls

[Daniel P. Berrange]

On Thu, Jul 21, 2016 at 01:05:59PM +0800, zhanghailiang wrote:
> Usage:
> (qemu) migrate file:/path/to/vm_statefile
> 
> Signed-off-by: zhanghailiang <zhang.zhanghailiang@huawei.com>
> Signed-off-by: Benoit Canet <benoit.canet@gmail.com>
> ---
>  include/migration/migration.h |  2 ++
>  migration/fd.c                | 34 ++++++++++++++++++++++++++++------
>  migration/migration.c         |  2 ++
>  migration/trace-events        |  1 +
>  4 files changed, 33 insertions(+), 6 deletions(-)
> 
> diff --git a/include/migration/migration.h b/include/migration/migration.h
> index 3c96623..cc2e4f6 100644
> --- a/include/migration/migration.h
> +++ b/include/migration/migration.h
> @@ -221,6 +221,8 @@ void fd_start_incoming_migration(const char *path, Error **errp);
>  
>  void fd_start_outgoing_migration(MigrationState *s, const char *fdname, Error **errp);
>  
> +void file_start_outgoing_migration(MigrationState *s, const char *filename, Error **errp);
> +
>  void rdma_start_outgoing_migration(void *opaque, const char *host_port, Error **errp);
>  
>  void rdma_start_incoming_migration(const char *host_port, Error **errp);
> diff --git a/migration/fd.c b/migration/fd.c
> index 84a10fd..fa5df67 100644
> --- a/migration/fd.c
> +++ b/migration/fd.c
> @@ -23,15 +23,11 @@
>  #include "trace.h"
>  
>  
> -void fd_start_outgoing_migration(MigrationState *s, const char *fdname, Error **errp)
> +static void fd_start_outgoing_migration_core(MigrationState *s, int fd,
> +                                             Error **errp)
>  {
>      QIOChannel *ioc;
> -    int fd = monitor_get_fd(cur_mon, fdname, errp);
> -    if (fd == -1) {
> -        return;
> -    }
>  
> -    trace_migration_fd_outgoing(fd);
>      ioc = qio_channel_new_fd(fd, errp);
>      if (!ioc) {
>          close(fd);
> @@ -42,6 +38,32 @@ void fd_start_outgoing_migration(MigrationState *s, const char *fdname, Error **
>      object_unref(OBJECT(ioc));
>  }
>  
> +void fd_start_outgoing_migration(MigrationState *s, const char *fdname, Error **errp)
> +{
> +    int fd = monitor_get_fd(cur_mon, fdname, errp);
> +    if (fd == -1) {
> +        return;
> +    }
> +
> +    trace_migration_fd_outgoing(fd);
> +    fd_start_outgoing_migration_core(s, fd, errp);
> +}
> +
> +void file_start_outgoing_migration(MigrationState *s, const char *filename,
> +                                   Error **errp)
> +{
> +    int fd;
> +
> +    fd = qemu_open(filename, O_CREAT | O_TRUNC | O_WRONLY, S_IRUSR | S_IWUSR);
> +    if (fd < 0) {
> +        error_setg_errno(errp, errno, "Failed to open file: %s", filename);
> +        return;
> +    }
> +    
> +    trace_migration_file_outgoing(filename);
> +    fd_start_outgoing_migration_core(s, fd, errp);
> +}

This isn't going to fly.

Annoyingly with plain files on POSIX platforms you can't get non-blocking
I/O, so even though we'll be setting the O_NONBLOCK on fd shortly, I/O is
still going to block the entire thread.  The same applies for file reads
wrt to your next patch supporting incoming mode.

Regards,
Daniel
-- 
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Re: [Qemu-devel] [RFC PATCH 0/2] Migration: support working on file:url

[Daniel P. Berrange]

On Thu, Jul 21, 2016 at 01:05:58PM +0800, zhanghailiang wrote:
> It is more simple to use file:url to migrate VM into file.
> Besides, it will be used in memory snapshot.

NB, you can already migrate into a file

   "exec:/bin/cat > /path/to/file"

and likewise

  qemu -incoming "exec:/bin/cat /path/to/file"

This avoids the problem with POSIX I/O on plain files not actually
supporting O_NONBLOCK in any sensible manner, which your file:
suggestion suffers from.

Regards,
Daniel
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Re: [Qemu-devel] [RFC PATCH 0/2] Migration: support working on file:url

[Dr. David Alan Gilbert]

* Daniel P. Berrange (berrange@redhat.com) wrote:
> On Thu, Jul 21, 2016 at 01:05:58PM +0800, zhanghailiang wrote:
> > It is more simple to use file:url to migrate VM into file.
> > Besides, it will be used in memory snapshot.
> 
> NB, you can already migrate into a file
> 
>    "exec:/bin/cat > /path/to/file"
> 
> and likewise
> 
>   qemu -incoming "exec:/bin/cat /path/to/file"
> 
> This avoids the problem with POSIX I/O on plain files not actually
> supporting O_NONBLOCK in any sensible manner, which your file:
> suggestion suffers from.

Hmm that's a shame; I liked this idea as a nice simplification of the
exec: stuff.

Dave

> Regards,
> Daniel
> -- 
> |: http://berrange.com      -o-    http://www.flickr.com/photos/dberrange/ :|
> |: http://libvirt.org              -o-             http://virt-manager.org :|
> |: http://autobuild.org       -o-         http://search.cpan.org/~danberr/ :|
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--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK

Re: [Qemu-devel] [RFC PATCH 0/2] Migration: support working on file:url

[Hailiang Zhang]

On 2016/7/21 20:19, Daniel P. Berrange wrote:
> On Thu, Jul 21, 2016 at 01:05:58PM +0800, zhanghailiang wrote:
>> It is more simple to use file:url to migrate VM into file.
>> Besides, it will be used in memory snapshot.
>
> NB, you can already migrate into a file
>
>     "exec:/bin/cat > /path/to/file"
>
> and likewise
>
>    qemu -incoming "exec:/bin/cat /path/to/file"
>
> This avoids the problem with POSIX I/O on plain files not actually
> supporting O_NONBLOCK in any sensible manner, which your file:
> suggestion suffers from.
>

OK, got it, please ignore this series. Thanks.

> Regards,
> Daniel
>

Re: [Qemu-devel] [RFC PATCH 0/2] Migration: support working on file:url

[Daniel P. Berrange]

On Thu, Jul 21, 2016 at 06:41:23PM +0100, Dr. David Alan Gilbert wrote:
> * Daniel P. Berrange (berrange@redhat.com) wrote:
> > On Thu, Jul 21, 2016 at 01:05:58PM +0800, zhanghailiang wrote:
> > > It is more simple to use file:url to migrate VM into file.
> > > Besides, it will be used in memory snapshot.
> > 
> > NB, you can already migrate into a file
> > 
> >    "exec:/bin/cat > /path/to/file"
> > 
> > and likewise
> > 
> >   qemu -incoming "exec:/bin/cat /path/to/file"
> > 
> > This avoids the problem with POSIX I/O on plain files not actually
> > supporting O_NONBLOCK in any sensible manner, which your file:
> > suggestion suffers from.
> 
> Hmm that's a shame; I liked this idea as a nice simplification of the
> exec: stuff.

The only way to achieve that would be to spawn a thread in QEMU that
does I/O to the actual file, and then have the migration code do I/O
to/from that thread via a pipe. IOW, the thread would take the role
of cat.  What that's worth doing or not I don't know, given that it
is already possible to use exec+cat.

Regards,
Daniel
-- 
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