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#include <assert.h>

atomic_t fs_handle_next = {

    .count = 1

};

     * In reply to the VFS_REGISTER request, we assign the client file

     * system a global file system handle.

    fs_info->fs_handle = (int) atomic_postinc(&fs_handle_next);

}

/** For a given file system handle, implement policy for allocating a phone.

 *

 * @param handle    File system handle.

 *

 * @return      Phone over which a multi-call request can be safely

 *          sent. Return 0 if no phone was found.

 */

int vfs_grab_phone(int handle)

{

    /*

     * For now, we don't try to be very clever and very fast.

     * We simply lookup the phone in the fs_head list. We currently don't

     * open any additional phones (even though that itself would be pretty

     * straightforward; housekeeping multiple open phones to a FS task would

     * be more demanding). Instead, we simply take the respective

     * phone_futex and keep it until vfs_release_phone().

     */

    futex_down(&fs_head_futex);

    link_t *cur;

    fs_info_t *fs;

    for (cur = fs_head.next; cur != &fs_head; cur = cur->next) {

        fs = list_get_instance(cur, fs_info_t, fs_link);

        if (fs->fs_handle == handle) {

            futex_up(&fs_head_futex);

            /*

             * For now, take the futex unconditionally.

             * Oh yeah, serialization rocks.

             * It will be up'ed in vfs_release_phone().

             */

            futex_down(&fs->phone_futex);

            return fs->phone;

        }

    }

    futex_up(&fs_head_futex);

    return 0;

}

/** Tell VFS that the phone is in use for any request.

 *

 * @param phone     Phone to FS task.

 */

void vfs_release_phone(int phone)

{

    bool found = false;

    futex_down(&fs_head_futex);

    link_t *cur;

    for (cur = fs_head.next; cur != &fs_head; cur = cur->next) {

        fs_info_t *fs = list_get_instance(cur, fs_info_t, fs_link);

        if (fs->phone == phone) {

            found = true;

            futex_up(&fs_head_futex);

            futex_up(&fs->phone_futex);

            return;

        }

    }

    futex_up(&fs_head_futex);

    /*

     * Not good to get here.

     */

    assert(found == true);