Re: [PATCH V11 05/15] block/export: track IOThread references

On Wed, Aug 12, 2026, 3:34 AM Stefan Hajnoczi <[email protected]> wrote:

> On Fri, Aug 07, 2026 at 04:25:14AM +0800, Zhang Chen wrote:
> > Track the IOThreads used by a block export and identify the holder
> > with the unique BlockExportOptions id.
> >
> > Acquire holder-aware references during export creation and release
> > them on error or export deletion.  Support both single- and
> > multi-iothread exports.
> >
> > Signed-off-by: Zhang Chen <[email protected]>
> > ---
> >  block/export/export.c  | 79 +++++++++++++++++++++++++++++++++++++-----
> >  include/block/export.h |  6 ++++
> >  2 files changed, 76 insertions(+), 9 deletions(-)
> >
> > diff --git a/block/export/export.c b/block/export/export.c
> > index b733f269f3..96d719418e 100644
> > --- a/block/export/export.c
> > +++ b/block/export/export.c
> > @@ -15,7 +15,6 @@
> >
> >  #include "block/block.h"
> >  #include "system/block-backend.h"
> > -#include "system/iothread.h"
> >  #include "block/export.h"
> >  #include "block/fuse.h"
> >  #include "block/nbd.h"
> > @@ -85,6 +84,8 @@ BlockExport *blk_exp_add(BlockExportOptions *export,
> Error **errp)
> >      AioContext *ctx;
> >      AioContext **multithread_ctxs = NULL;
> >      size_t multithread_count = 0;
> > +    g_autofree IOThread **local_iothreads = NULL;
> > +    const char *holder_id = NULL;
> >      uint64_t perm;
> >      int ret;
> >
> > @@ -139,7 +140,16 @@ BlockExport *blk_exp_add(BlockExportOptions
> *export, Error **errp)
> >              goto fail;
> >          }
> >
> > -        new_ctx = iothread_get_aio_context(iothread);
> > +        holder_id = export->id;
> > +        const IOThreadHolder holder = {
> > +            .type = IO_THREAD_HOLDER_KIND_BLOCK_EXPORT,
> > +            .u.block_export.export_id = (char *)holder_id,
>
> Is this char * cast necessary since the holder variable is declared
> const?
>
>
>
OK，will fix it in v12.

Thanks
Chen


> > +        };
> > +
> > +        new_ctx = iothread_ref_and_get_aio_context(iothread, &holder);
> > +        multithread_count = 1;
> > +        local_iothreads = g_new0(IOThread *, 1);
> > +        local_iothreads[0] = iothread;
> >
> >          /* Ignore errors with fixed-iothread=false */
> >          set_context_errp = fixed_iothread ? errp : NULL;
> > @@ -163,8 +173,15 @@ BlockExport *blk_exp_add(BlockExportOptions
> *export, Error **errp)
> >              return NULL;
> >          }
> >
> > +        local_iothreads = g_new0(IOThread *, multithread_count);
> >          multithread_ctxs = g_new(AioContext *, multithread_count);
> >          i = 0;
> > +        holder_id = export->id;
> > +        const IOThreadHolder holder = {
> > +            .type = IO_THREAD_HOLDER_KIND_BLOCK_EXPORT,
> > +            .u.block_export.export_id = (char *)holder_id,
>
> Same here.
>
> > +        };
> > +
> >          for (strList *e = iothread_list; e; e = e->next) {
> >              IOThread *iothread = iothread_by_id(e->value);
> >
> > @@ -172,7 +189,9 @@ BlockExport *blk_exp_add(BlockExportOptions *export,
> Error **errp)
> >                  error_setg(errp, "iothread \"%s\" not found", e->value);
> >                  goto fail;
> >              }
> > -            multithread_ctxs[i++] = iothread_get_aio_context(iothread);
> > +            local_iothreads[i] = iothread;
> > +            multithread_ctxs[i++] =
> iothread_ref_and_get_aio_context(iothread,
> > +
>  &holder);
> >          }
> >          assert(i == multithread_count);
> >      }
> > @@ -225,12 +244,15 @@ BlockExport *blk_exp_add(BlockExportOptions
> *export, Error **errp)
> >      assert(drv->instance_size >= sizeof(BlockExport));
> >      exp = g_malloc0(drv->instance_size);
> >      *exp = (BlockExport) {
> > -        .drv        = drv,
> > -        .refcount   = 1,
> > -        .user_owned = true,
> > -        .id         = g_strdup(export->id),
> > -        .ctx        = ctx,
> > -        .blk        = blk,
> > +        .drv                  = drv,
> > +        .refcount             = 1,
> > +        .user_owned           = true,
> > +        .id                   = g_strdup(export->id),
> > +        .ctx                  = ctx,
> > +        .blk                  = blk,
> > +        .iothreads            = g_steal_pointer(&local_iothreads),
> > +        .iothread_count       = multithread_count,
> > +        .iothread_holder_id   = g_strdup(holder_id),
> >      };
> >
> >      ret = drv->create(exp, export, multithread_ctxs, multithread_count,
> errp);
> > @@ -250,8 +272,32 @@ fail:
> >          blk_unref(blk);
> >      }
> >      if (exp) {
> > +        if (exp->iothreads) {
> > +            const IOThreadHolder holder = {
> > +                .type = IO_THREAD_HOLDER_KIND_BLOCK_EXPORT,
> > +                .u.block_export.export_id = exp->iothread_holder_id,
> > +            };
> > +            for (size_t j = 0; j < exp->iothread_count; j++) {
> > +                if (exp->iothreads[j]) {
> > +                    iothread_put_aio_context(exp->iothreads[j],
> &holder);
> > +                }
> > +            }
> > +            g_free(exp->iothreads);
> > +        }
> > +        g_free(exp->iothread_holder_id);
> >          g_free(exp->id);
> >          g_free(exp);
> > +    } else if (local_iothreads) {
> > +        const IOThreadHolder holder = {
> > +            .type = IO_THREAD_HOLDER_KIND_BLOCK_EXPORT,
> > +            .u.block_export.export_id = (char *)holder_id,
>
> Same here.
>
> > +        };
> > +
> > +        for (size_t j = 0; j < multithread_count; j++) {
> > +            if (local_iothreads[j]) {
> > +                iothread_put_aio_context(local_iothreads[j], &holder);
> > +            }
> > +        }
> >      }
> >      g_free(multithread_ctxs);
> >      return NULL;
> > @@ -269,10 +315,25 @@ static void blk_exp_delete_bh(void *opaque)
> >      BlockExport *exp = opaque;
> >
> >      assert(exp->refcount == 0);
> > +
> >      QLIST_REMOVE(exp, next);
> >      exp->drv->delete(exp);
> >      blk_set_dev_ops(exp->blk, NULL, NULL);
> >      blk_unref(exp->blk);
> > +
> > +    if (exp->iothreads) {
> > +        const IOThreadHolder holder = {
> > +            .type = IO_THREAD_HOLDER_KIND_BLOCK_EXPORT,
> > +            .u.block_export.export_id = exp->iothread_holder_id,
> > +        };
> > +
> > +        for (size_t i = 0; i < exp->iothread_count; i++) {
> > +            iothread_put_aio_context(exp->iothreads[i], &holder);
> > +        }
> > +        g_free(exp->iothreads);
> > +    }
> > +
> > +    g_free(exp->iothread_holder_id);
> >      qapi_event_send_block_export_deleted(exp->id);
> >      g_free(exp->id);
> >      g_free(exp);
> > diff --git a/include/block/export.h b/include/block/export.h
> > index ca45da928c..a093dea0b6 100644
> > --- a/include/block/export.h
> > +++ b/include/block/export.h
> > @@ -16,6 +16,7 @@
> >
> >  #include "qapi/qapi-types-block-export.h"
> >  #include "qemu/queue.h"
> > +#include "system/iothread.h"
> >
> >  typedef struct BlockExport BlockExport;
> >
> > @@ -89,6 +90,11 @@ struct BlockExport {
> >
> >      /* List entry for block_exports */
> >      QLIST_ENTRY(BlockExport) next;
> > +
> > +    /* The IOThreads utilized by this specific block export */
> > +    IOThread **iothreads;
> > +    size_t iothread_count;
> > +    char *iothread_holder_id;
> >  };
> >
> >  BlockExport *blk_exp_add(BlockExportOptions *export, Error **errp);
> > --
> > 2.53.0
> >
>