Re: [PATCH 2/8] plugins: version 2, require unique plugin names

["Alex Bennée" <alex.bennee@linaro.org>]

Andrew Fasano <fasano@mit.edu> writes:

> From: Elysia Witham <elysia.witham@ll.mit.edu>
>
> In order for the QPP API to resolve interactions between plugins,
> plugins must export their own names which cannot match any other
> loaded plugins.
>
> Signed-off-by: Elysia Witham <elysia.witham@ll.mit.edu>
> Signed-off-by: Andrew Fasano <fasano@mit.edu>
> ---
>  include/qemu/qemu-plugin.h |  2 +-
>  plugins/core.c             | 12 +++++++++
>  plugins/loader.c           | 50 +++++++++++++++++++++++++++++++++-----
>  plugins/plugin.h           |  7 ++++++
>  tests/plugin/bb.c          |  1 +
>  tests/plugin/empty.c       |  1 +
>  tests/plugin/insn.c        |  1 +
>  tests/plugin/mem.c         |  1 +
>  tests/plugin/syscall.c     |  1 +
>  9 files changed, 69 insertions(+), 7 deletions(-)
>
> diff --git a/include/qemu/qemu-plugin.h b/include/qemu/qemu-plugin.h
> index d0e9d03adf..5326f33ce8 100644
> --- a/include/qemu/qemu-plugin.h
> +++ b/include/qemu/qemu-plugin.h
> @@ -51,7 +51,7 @@ typedef uint64_t qemu_plugin_id_t;
>  
>  extern QEMU_PLUGIN_EXPORT int qemu_plugin_version;
>  
> -#define QEMU_PLUGIN_VERSION 1
> +#define QEMU_PLUGIN_VERSION 2
>  
>  /**
>   * struct qemu_info_t - system information for plugins
> diff --git a/plugins/core.c b/plugins/core.c
> index ccb770a485..5fbdcb5768 100644
> --- a/plugins/core.c
> +++ b/plugins/core.c
> @@ -236,6 +236,18 @@ void qemu_plugin_vcpu_exit_hook(CPUState *cpu)
>      qemu_rec_mutex_unlock(&plugin.lock);
>  }
>  
> +int name_to_plugin_version(const char *name)
> +{
> +    struct qemu_plugin_ctx *ctx;
> +    QTAILQ_FOREACH(ctx, &plugin.ctxs, entry) {
> +        if (strcmp(ctx->name, name) == 0) {
> +            return ctx->version;
> +        }
> +    }
> +    warn_report("Could not find any plugin named %s.", name);
> +    return -1;
> +}
> +

This function seems to be unused.

>  struct plugin_for_each_args {
>      struct qemu_plugin_ctx *ctx;
>      qemu_plugin_vcpu_simple_cb_t cb;
> diff --git a/plugins/loader.c b/plugins/loader.c
> index 88c30bde2d..12c0680e03 100644
> --- a/plugins/loader.c
> +++ b/plugins/loader.c
> @@ -177,7 +177,7 @@ QEMU_DISABLE_CFI
>  static int plugin_load(struct qemu_plugin_desc *desc, const qemu_info_t *info, Error **errp)
>  {
>      qemu_plugin_install_func_t install;
> -    struct qemu_plugin_ctx *ctx;
> +    struct qemu_plugin_ctx *ctx, *ctx2;
>      gpointer sym;
>      int rc;
>  
> @@ -208,17 +208,55 @@ static int plugin_load(struct qemu_plugin_desc *desc, const qemu_info_t *info, E
>                     desc->path, g_module_error());
>          goto err_symbol;
>      } else {
> -        int version = *(int *)sym;
> -        if (version < QEMU_PLUGIN_MIN_VERSION) {
> +        ctx->version = *(int *)sym;
> +        if (ctx->version < QEMU_PLUGIN_MIN_VERSION) {
>              error_setg(errp, "Could not load plugin %s: plugin requires API version %d, but "
>                         "this QEMU supports only a minimum version of %d",
> -                       desc->path, version, QEMU_PLUGIN_MIN_VERSION);
> +                       desc->path, ctx->version, QEMU_PLUGIN_MIN_VERSION);
>              goto err_symbol;
> -        } else if (version > QEMU_PLUGIN_VERSION) {
> +        } else if (ctx->version > QEMU_PLUGIN_VERSION) {
>              error_setg(errp, "Could not load plugin %s: plugin requires API version %d, but "
>                         "this QEMU supports only up to version %d",
> -                       desc->path, version, QEMU_PLUGIN_VERSION);
> +                       desc->path, ctx->version, QEMU_PLUGIN_VERSION);
>              goto err_symbol;
> +        } else if (ctx->version < QPP_MINIMUM_VERSION) {
> +            ctx->name = NULL;

A comment wouldn't go amiss here. Something like:

  "Older plugins will not be available for QPP calls".

> +        } else {
> +            if (!g_module_symbol(ctx->handle, "qemu_plugin_name", &sym)) {
> +                error_setg(errp, "Could not load plugin %s: plugin does not "
> +                           "declare plugin name %s",
> +                           desc->path, g_module_error());
> +                goto err_symbol;
> +            }
> +            ctx->name = (const char *)strdup(*(const char **)sym);
> +            QTAILQ_FOREACH(ctx2, &plugin.ctxs, entry) {
> +                if (strcmp(ctx2->name, ctx->name) == 0) {
> +                    error_setg(errp, "Could not load plugin %s as the name %s "
> +                               "is already in use by plugin at %s",
> +                               desc->path, ctx->name, ctx2->desc->path);
> +                    goto err_symbol;
> +                }
> +            }
> +            if (g_module_symbol(ctx->handle, "qemu_plugin_uses", &sym)) {
> +                const char **dependencies = &(*(const char **)sym);
> +                bool found = false;
> +                while (*dependencies) {
> +                    found = false;
> +                    QTAILQ_FOREACH(ctx2, &plugin.ctxs, entry) {
> +                        if (strcmp(ctx2->name, *dependencies) == 0) {

Lets use glib where we can, in this case g_strcmp0().

> +                            dependencies++;
> +                            found = true;
> +                            break;
> +                        }
> +                    }
> +                    if (!found) {
> +                        error_setg(errp, "Could not load plugin %s as it is "
> +                                   "dependent on %s which is not loaded",
> +                                   ctx->name, *dependencies);
> +                        goto err_symbol;
> +                    }

We are implying a load order here which we should document. Ideally we
could avoid it but I suspect that requires too much hoop jumping.

> +                }
> +            }
>          }
>      }
>  
> diff --git a/plugins/plugin.h b/plugins/plugin.h
> index 5eb2fdbc85..ce885bfa98 100644
> --- a/plugins/plugin.h
> +++ b/plugins/plugin.h
> @@ -16,6 +16,7 @@
>  #include "qemu/qht.h"
>  
>  #define QEMU_PLUGIN_MIN_VERSION 0
> +#define QPP_MINIMUM_VERSION 2
>  
>  /* global state */
>  struct qemu_plugin_state {
> @@ -50,6 +51,8 @@ struct qemu_plugin_state {
>  struct qemu_plugin_ctx {
>      GModule *handle;
>      qemu_plugin_id_t id;
> +    const char *name;
> +    int version;
>      struct qemu_plugin_cb *callbacks[QEMU_PLUGIN_EV_MAX];
>      QTAILQ_ENTRY(qemu_plugin_ctx) entry;
>      /*
> @@ -64,6 +67,8 @@ struct qemu_plugin_ctx {
>  
>  struct qemu_plugin_ctx *plugin_id_to_ctx_locked(qemu_plugin_id_t id);
>  
> +struct qemu_plugin_ctx *plugin_name_to_ctx_locked(const char* name);
> +
>  void plugin_register_inline_op(GArray **arr,
>                                 enum qemu_plugin_mem_rw rw,
>                                 enum qemu_plugin_op op, void *ptr,
> @@ -97,4 +102,6 @@ void plugin_register_vcpu_mem_cb(GArray **arr,
>  
>  void exec_inline_op(struct qemu_plugin_dyn_cb *cb);
>  
> +int name_to_plugin_version(const char *name);
> +
>  #endif /* PLUGIN_H */
> diff --git a/tests/plugin/bb.c b/tests/plugin/bb.c
> index 7d470a1011..c04e5aaf90 100644
> --- a/tests/plugin/bb.c
> +++ b/tests/plugin/bb.c
> @@ -15,6 +15,7 @@
>  #include <qemu-plugin.h>
>  
>  QEMU_PLUGIN_EXPORT int qemu_plugin_version = QEMU_PLUGIN_VERSION;
> +QEMU_PLUGIN_EXPORT const char *qemu_plugin_name = "bb";
>  
>  typedef struct {
>      GMutex lock;
> diff --git a/tests/plugin/empty.c b/tests/plugin/empty.c
> index 8fa6bacd93..0f3d2b92b9 100644
> --- a/tests/plugin/empty.c
> +++ b/tests/plugin/empty.c
> @@ -14,6 +14,7 @@
>  #include <qemu-plugin.h>
>  
>  QEMU_PLUGIN_EXPORT int qemu_plugin_version = QEMU_PLUGIN_VERSION;
> +QEMU_PLUGIN_EXPORT const char *qemu_plugin_name = "empty";
>  
>  /*
>   * Empty TB translation callback.
> diff --git a/tests/plugin/insn.c b/tests/plugin/insn.c
> index cd5ea5d4ae..3f71138139 100644
> --- a/tests/plugin/insn.c
> +++ b/tests/plugin/insn.c
> @@ -15,6 +15,7 @@
>  #include <qemu-plugin.h>
>  
>  QEMU_PLUGIN_EXPORT int qemu_plugin_version = QEMU_PLUGIN_VERSION;
> +QEMU_PLUGIN_EXPORT const char *qemu_plugin_name = "insn";
>  
>  #define MAX_CPUS 8 /* lets not go nuts */
>  
> diff --git a/tests/plugin/mem.c b/tests/plugin/mem.c
> index 4570f7d815..35e5d7fe2a 100644
> --- a/tests/plugin/mem.c
> +++ b/tests/plugin/mem.c
> @@ -15,6 +15,7 @@
>  #include <qemu-plugin.h>
>  
>  QEMU_PLUGIN_EXPORT int qemu_plugin_version = QEMU_PLUGIN_VERSION;
> +QEMU_PLUGIN_EXPORT const char *qemu_plugin_name = "mem";
>  
>  static uint64_t inline_mem_count;
>  static uint64_t cb_mem_count;
> diff --git a/tests/plugin/syscall.c b/tests/plugin/syscall.c
> index 96040c578f..922bdbd2e6 100644
> --- a/tests/plugin/syscall.c
> +++ b/tests/plugin/syscall.c
> @@ -15,6 +15,7 @@
>  #include <qemu-plugin.h>
>  
>  QEMU_PLUGIN_EXPORT int qemu_plugin_version = QEMU_PLUGIN_VERSION;
> +QEMU_PLUGIN_EXPORT const char *qemu_plugin_name = "syscall";
>  
>  typedef struct {
>      int64_t num;

You should update the plugins in contrib/plugins as well.

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro