[MacPorts] #64909: libaacs for PowerPC: how to rewrite __block code in standard C?

[MacPorts]

#64909: libaacs for PowerPC: how to rewrite __block code in standard C?
---------------------------+-------------------------------------------
  Reporter:  barracuda156  |      Owner:  i0ntempest
      Type:  defect        |     Status:  assigned
  Priority:  Normal        |  Milestone:
 Component:  ports         |    Version:  2.7.2
Resolution:                |   Keywords:  powerpc, leopard, snowleopard
      Port:  libaacs       |
---------------------------+-------------------------------------------
Changes (by ryandesign):

 * status:  new => assigned
 * owner:  (none) => i0ntempest
 * type:  request => defect


Old description:

> Could anyone advise me if this can be rewritten in standard C? gcc does
> not process this __block code correctly:
>

> {{{
> void device_close(MMCDEV **pp)
> {
>     __block int rc = 0;
>     if (pp && *pp) {
>         MMCDEV *mmc = *pp;
>
>         /* When the exclusive access to the drive is released,
>          * the OS will see the device like a "new" device and
>          * try to mount it. Therefore we can't just mount the
>          * disk we previously got immediately here as it would
>          * fail with kDAReturnBadArgument as the disk is not
>          * available yet.
>          * Trying to mount the disk after it appears in peek
>          * does not work either as the disk is not yet ready
>          * or in the process of being mounted by the OS so
>          * that would return an kDAReturnBusy error.
>          * The only way that seems to reliably work is to use
>          * a mount approval callback. When the OS tries to
>          * mount the disk, the mount approval callback is
>          * called and we can reject mounting and then proceed
>          * to mount the disk ourselves.
>          * Claiming exclusive access using DADiskClaim in order
>          * to prevent the OS form mounting the disk does not work
>          * either!
>          */
>
>         if (mmc->taskInterface) {
> (*mmc->taskInterface)->ReleaseExclusiveAccess(mmc->taskInterface);
>             (*mmc->taskInterface)->Release(mmc->taskInterface);
>             mmc->taskInterface = NULL;
>         }
>
>         if (mmc->mmcInterface) {
>             (*mmc->mmcInterface)->Release(mmc->mmcInterface);
>             mmc->mmcInterface = NULL;
>         }
>
>         if (mmc->plugInInterface) {
>             IODestroyPlugInInterface(mmc->plugInInterface);
>         }
>
>         if (!mmc->sync_sem) {
>             /* open failed before iokit_da_init() */
>             X_FREE(*pp);
>             return;
>         }
>
>         /* Wait for disc to re-appear for 20 seconds.
>          * This timeout was figured out by experimentation with
>          * a USB BD drive which sometimes can take really long to
>          * be in a mountable state again.
>          * For internal drives this is probably much faster
>          * so the long timeout shouldn't do much harm for thse
>          * cases.
>          */
>         dispatch_time_t timeout = dispatch_time(DISPATCH_TIME_NOW, 20 *
> 1E+9);
>         dispatch_semaphore_wait(mmc->sync_sem, timeout);
>
>         /* It is crucial that this is done on the event handling queue
>          * else callbacks could be received while this code runs.
>          */
>         dispatch_sync(mmc->background_queue, ^{
>             if (disk_appeared != mmc->disk_state) {
>                 BD_DEBUG(DBG_MMC | DBG_CRIT, "Timeout waiting for the
> disc to appear again!\n");
>                 iokit_da_destroy(mmc);
>                 rc = -1;
>                 return;
>             }
>             rc = 0;
>         });
>
>         if (rc == 0) {
>             /* Disk appeared successfully, mount it.
>              * Return value is ignored as logging of success or
>              * error takes place in the callback already and there
>              * is nothing we can do really if mounting fails.
>              */
>             (void) iokit_mount(mmc);
>             iokit_da_destroy(mmc);
>         }
>         X_FREE(*pp);
>     }
> }
> }}}
>
> This is from `src/file/mmc_device_darwin.c`.

New description:

 Could anyone advise me if this can be rewritten in standard C? gcc does
 not process this `__block` code correctly:


 {{{
 void device_close(MMCDEV **pp)
 {
     __block int rc = 0;
     if (pp && *pp) {
         MMCDEV *mmc = *pp;

         /* When the exclusive access to the drive is released,
          * the OS will see the device like a "new" device and
          * try to mount it. Therefore we can't just mount the
          * disk we previously got immediately here as it would
          * fail with kDAReturnBadArgument as the disk is not
          * available yet.
          * Trying to mount the disk after it appears in peek
          * does not work either as the disk is not yet ready
          * or in the process of being mounted by the OS so
          * that would return an kDAReturnBusy error.
          * The only way that seems to reliably work is to use
          * a mount approval callback. When the OS tries to
          * mount the disk, the mount approval callback is
          * called and we can reject mounting and then proceed
          * to mount the disk ourselves.
          * Claiming exclusive access using DADiskClaim in order
          * to prevent the OS form mounting the disk does not work
          * either!
          */

         if (mmc->taskInterface) {
 (*mmc->taskInterface)->ReleaseExclusiveAccess(mmc->taskInterface);
             (*mmc->taskInterface)->Release(mmc->taskInterface);
             mmc->taskInterface = NULL;
         }

         if (mmc->mmcInterface) {
             (*mmc->mmcInterface)->Release(mmc->mmcInterface);
             mmc->mmcInterface = NULL;
         }

         if (mmc->plugInInterface) {
             IODestroyPlugInInterface(mmc->plugInInterface);
         }

         if (!mmc->sync_sem) {
             /* open failed before iokit_da_init() */
             X_FREE(*pp);
             return;
         }

         /* Wait for disc to re-appear for 20 seconds.
          * This timeout was figured out by experimentation with
          * a USB BD drive which sometimes can take really long to
          * be in a mountable state again.
          * For internal drives this is probably much faster
          * so the long timeout shouldn't do much harm for thse
          * cases.
          */
         dispatch_time_t timeout = dispatch_time(DISPATCH_TIME_NOW, 20 *
 1E+9);
         dispatch_semaphore_wait(mmc->sync_sem, timeout);

         /* It is crucial that this is done on the event handling queue
          * else callbacks could be received while this code runs.
          */
         dispatch_sync(mmc->background_queue, ^{
             if (disk_appeared != mmc->disk_state) {
                 BD_DEBUG(DBG_MMC | DBG_CRIT, "Timeout waiting for the disc
 to appear again!\n");
                 iokit_da_destroy(mmc);
                 rc = -1;
                 return;
             }
             rc = 0;
         });

         if (rc == 0) {
             /* Disk appeared successfully, mount it.
              * Return value is ignored as logging of success or
              * error takes place in the callback already and there
              * is nothing we can do really if mounting fails.
              */
             (void) iokit_mount(mmc);
             iokit_da_destroy(mmc);
         }
         X_FREE(*pp);
     }
 }
 }}}

 This is from `src/file/mmc_device_darwin.c`.

--

Comment:

 FYI:

 Here's what blocks are:
 https://en.wikipedia.org/wiki/Blocks_(C_language_extension)

 Here's the ticket about gcc not supporting them yet:
 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78352

 Probably the only sane path forward for this is for gcc to implement
 support for blocks. Then this port can use gcc to build on PowerPC. It's
 probably unreasonable to expect upstream to abandon the useful blocks
 feature in their code for the benefit of ancient systems, and it's
 probably unreasonable for MacPorts to develop and carry forward forever a
 large patch for this.

-- 
Ticket URL: <https://trac.macports.org/ticket/64909#comment:1>
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