Re: [PATCH v2 4/6] migration: Avoid multiple parsing of uri in migration code flow

["Daniel P. Berrangé" <berrange@redhat.com>]

On Wed, Feb 08, 2023 at 09:35:58AM +0000, Het Gala wrote:
> In existing senario, 'migrate' QAPI argument - string uri, is encoded
> twice to extract migration parameters for stream connection. This is
> not a good representation of migration wire protocol as it is a data
> encoding scheme within a data encoding scheme. Qemu should be able to
> directly work with results from QAPI without having to do a second
> level parsing.
> Modified 'migrate' QAPI design supports well defined MigrateChannel
> struct which plays important role in avoiding double encoding
> of uri strings.
> 
> qemu_uri_parsing() parses uri string (kept for backward
> compatibility) and populate the MigrateChannel struct parameters.
> Migration code flow for all required migration transport types -
> socket, exec and rdma is modified.
> 
> Suggested-by: Daniel P. Berrange <berrange@redhat.com>
> Suggested-by: Manish Mishra <manish.mishra@nutanix.com>
> Suggested-by: Aravind Retnakaran <aravind.retnakaran@nutanix.com>
> Signed-off-by: Het Gala <het.gala@nutanix.com>
> ---
>  migration/exec.c      | 31 ++++++++++++++++--
>  migration/exec.h      |  4 ++-
>  migration/migration.c | 75 +++++++++++++++++++++++++++++++++++--------
>  migration/rdma.c      | 30 +++++------------
>  migration/rdma.h      |  3 +-
>  migration/socket.c    | 21 ++++--------
>  migration/socket.h    |  3 +-
>  7 files changed, 110 insertions(+), 57 deletions(-)
> 
> diff --git a/migration/exec.c b/migration/exec.c
> index 375d2e1b54..4fa9819792 100644
> --- a/migration/exec.c
> +++ b/migration/exec.c
> @@ -23,14 +23,39 @@
>  #include "migration.h"
>  #include "io/channel-command.h"
>  #include "trace.h"
> +#include "qapi/error.h"
>  
>  
> -void exec_start_outgoing_migration(MigrationState *s, const char *command, Error **errp)
> +void init_exec_array(strList *command, const char *argv[], Error **errp)
> +{
> +    int i = 0;
> +    strList *lst;
> +
> +    for (lst = command; lst ; lst = lst->next) {
> +        argv[i++] = lst->value;
> +    }
> +
> +    /*
> +     * Considering exec command always has 3 arguments to execute
> +     * a command directly from the bash itself.
> +     */
> +    if (i > 3) {
> +        error_setg(errp, "exec accepts maximum of 3 arguments in the list");
> +        return;
> +    }
> +
> +    argv[i] = NULL;
> +    return;
> +}
> +
> +void exec_start_outgoing_migration(MigrationState *s, strList *command,
> +                                   Error **errp)
>  {
>      QIOChannel *ioc;
> -    const char *argv[] = { "/bin/sh", "-c", command, NULL };
> +    const char *argv[4];
> +    init_exec_array(command, argv, errp);
>  
> -    trace_migration_exec_outgoing(command);
> +    trace_migration_exec_outgoing(argv[2]);
>      ioc = QIO_CHANNEL(qio_channel_command_new_spawn(argv,
>                                                      O_RDWR,
>                                                      errp));
> diff --git a/migration/exec.h b/migration/exec.h
> index b210ffde7a..5b39ba6cbb 100644
> --- a/migration/exec.h
> +++ b/migration/exec.h
> @@ -19,8 +19,10 @@
>  
>  #ifndef QEMU_MIGRATION_EXEC_H
>  #define QEMU_MIGRATION_EXEC_H
> +void init_exec_array(strList *command, const char *argv[], Error **errp);
> +
>  void exec_start_incoming_migration(const char *host_port, Error **errp);
>  
> -void exec_start_outgoing_migration(MigrationState *s, const char *host_port,
> +void exec_start_outgoing_migration(MigrationState *s, strList *host_port,
>                                     Error **errp);
>  #endif
> diff --git a/migration/migration.c b/migration/migration.c
> index f6dd8dbb03..accbf72a18 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -63,6 +63,7 @@
>  #include "sysemu/cpus.h"
>  #include "yank_functions.h"
>  #include "sysemu/qtest.h"
> +#include "qemu/sockets.h"
>  #include "ui/qemu-spice.h"
>  
>  #define MAX_THROTTLE  (128 << 20)      /* Migration transfer speed throttling */
> @@ -489,6 +490,44 @@ void migrate_add_address(SocketAddress *address)
>                        QAPI_CLONE(SocketAddress, address));
>  }
>  
> +static bool migrate_uri_parse(const char *uri,
> +                              MigrateChannel **channel,
> +                              Error **errp)
> +{
> +    Error *local_err = NULL;
> +    MigrateChannel *val = g_new0(MigrateChannel, 1);
> +    MigrateAddress *addrs = g_new0(MigrateAddress, 1);
> +    SocketAddress *saddr = g_new0(SocketAddress, 1);
> +    InetSocketAddress *isock = g_new0(InetSocketAddress, 1);
> +
> +    if (strstart(uri, "exec:", NULL)) {
> +        addrs->transport = MIGRATE_TRANSPORT_EXEC;
> +        addrs->u.exec.data = str_split_at_comma(uri + strlen("exec:"));

Huh, what is the purpose of using 'str_split_at_comma' ? The format
of this is  "exec:<shell command>", because it is run as:

     const char *argv[] = { "/bin/sh", "-c", command, NULL };

we should not be trying to parse the bit after 'exec:' at all,
and certainly not splitting it on commas which makes no sense
for a shell command.

I would have expected something more like this:

    strList **tail = &addrs->u.exec.data;
    QAPI_LIST_APPEND(tail, g_strdup("/bin/sh"));
    QAPI_LIST_APPEND(tail, g_strdup("-c"));
    QAPI_LIST_APPEND(tail, g_strdup(uri + strlen("exec:")));


> +    addrs = channel->addr;
> +    saddr = channel->addr->u.socket.socket_type;
> +    if (addrs->transport == MIGRATE_TRANSPORT_SOCKET) {
> +        if (saddr->type == SOCKET_ADDRESS_TYPE_INET ||
> +            saddr->type == SOCKET_ADDRESS_TYPE_UNIX ||
> +            saddr->type == SOCKET_ADDRESS_TYPE_VSOCK) {
> +            migrate_protocol_allow_multi_channels(true);
> +            socket_start_outgoing_migration(s, saddr, &local_err);
> +        } else if (saddr->type == SOCKET_ADDRESS_TYPE_FD) {
> +            fd_start_outgoing_migration(s, saddr->u.fd.str, &local_err);

This is probably a sign that  fd_start_outgoing_migration() should
be folded into the socket_start_outgoing_migration() method, but
that's a separate cleanup from this patch.

> +        }
> +    #ifdef CONFIG_RDMA
> +    } else if (addrs->transport == MIGRATE_TRANSPORT_RDMA) {
> +        rdma_start_outgoing_migration(s, addrs->u.rdma.data, &local_err);
> +    #endif
> +    } else if (addrs->transport == MIGRATE_TRANSPORT_EXEC) {
> +        exec_start_outgoing_migration(s, addrs->u.exec.data, &local_err);
>      } else {
>          if (!(has_resume && resume)) {
>              yank_unregister_instance(MIGRATION_YANK_INSTANCE);

With regards,
Daniel
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