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The door_call() function invokes the function associated with the door descriptor d, and passes the arguments (if any) specified in params. All of the params members are treated as in/out parameters during
a door invocation and may be updated upon returning from a door call. Passing NULL for params indicates there are no arguments to be passed and no results expected.
Arguments are specified using the data_ptr and desc_ptr members of params. The size of the argument data in bytes is passed in data_size and the number of argument descriptors is passed in desc_num.
Results from the door invocation are placed in the buffer, rbuf. See door_return(3DOOR). The data_ptr and desc_ptr members
of params are updated to reflect the location of the results within the rbuf buffer. The size of the data results and number of descriptors returned are updated in the data_size and desc_num members. It is acceptable to
use the same buffer for input argument data and results, so door_call() may be called with data_ptr and desc_ptr pointing to the buffer rbuf.
If the results of a door invocation exceed the size of the buffer specified by rsize, the system automatically allocates a new buffer in the caller's address space and updates the rbuf and rsize members to reflect this location. In this
case, the caller is responsible for reclaiming this area using munmap(rbuf, rsize) when the buffer is no longer required. See munmap(2).
Descriptors passed in a door_desc_t structure are identified by the d_attributes member. The client marks the d_attributes member with the type of object being passed by logically OR-ing the value of object type. Currently, the only object
type that can be passed or returned is a file descriptor, denoted by the DOOR_DESCRIPTOR attribute. Additionally, the DOOR_RELEASE attribute can be set, causing the descriptor to be closed in the caller's address space after it is passed to
the target. The descriptor will be closed even if door_call() returns an error, unless that error is EFAULT or EBADF.
The door_desc_t structure includes the following members:
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typedef struct {
door_attr_t d_attributes; /* Describes the parameter */
union {
struct {
int d_descriptor; /* Descriptor */
door_id_t d_id; /* Unique door id */
} d_desc;
} d_data;
} door_desc_t;
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When file descriptors are passed or returned, a new descriptor is created in the target address space and the d_descriptor member in the target argument is updated to reflect the new descriptor. In addition, the system passes a system-wide unique number associated with each door
in the door_id member and marks the d_attributes member with other attributes associated with a door including the following:
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DOOR_LOCAL
- The door received was created by this process using door_create(). See door_create(3DOOR).
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DOOR_PRIVATE
- The door received has a private pool of server threads associated with the door.
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DOOR_UNREF
- The door received is expecting an unreferenced notification.
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DOOR_UNREF_MULTI
- Similar to DOOR_UNREF, except multiple unreferenced notifications may be delivered for the same door.
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DOOR_REVOKED
- The door received has been revoked by the server.
The door_call() function is not a restartable system call. It returns EINTR if a signal was caught and handled by this thread. If the door invocation is not idempotent the caller should mask any signals that may be generated during a door_call() operation. If the client aborts in the middle of a door_call(), the server thread is notified using the POSIX (see standards(5))
thread cancellation mechanism. See cancellation(3THR).
The descriptor returned from door_create() is marked as close on exec (FD_CLOEXEC). Information about a door is available for all clients of a door using door_info(). Applications concerned with security should not place secure information
in door data that is accessible by door_info(). In particular, secure data should not be stored in the data item cookie. See door_info(3DOOR).
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