system/fidl/fuchsia-sysmem/allocator.fidl

// Copyright 2018 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

library fuchsia.sysmem;

using zx;

// Allocates system memory buffers.
//
// Needs Layout = "Simple" because used with "FIDL Simple C Bindings".
[Discoverable, Layout = "Simple"]
interface Allocator {
    // Allocates a collection of buffers on behalf of a single client.
    //
    // |bufferCount| indicates how many buffers to allocate, between 1 and 64.
    // |spec| describes constraints for allocating buffers of some
    // desired form.
    // |usage| describes how the client intends to access the buffers.
    // |collection| provides access to the allocated buffers.
    //
    // Returns |ZX_OK| if successful.
    // Returns |ZX_ERR_NO_MEMORY| if the request is valid but cannot be
    // fulfilled due to resource exhaustion.
    // Returns |ZX_ERR_ACCESS_DENIED| if the caller is not permitted to
    // obtain the buffers it requested.
    // Returns |ZX_ERR_INVALID_ARGS| if the request is malformed.
    // Returns |ZX_ERR_NOT_SUPPORTED| if request is valid but cannot be
    // satisfied, perhaps due to hardware limitations.
    1: AllocateCollection(uint32 buffer_count,
                          BufferSpec spec,
                          BufferUsage usage)
           -> (zx.status status, BufferCollectionInfo collection);

    // Allocates a collection of buffers which will be shared among one
    // or more clients.  This operation occurs in two phases (which may
    // happen concurrently).
    //
    // |bufferCount| indicates how many buffers to allocate, between 1 and 64.
    // |spec| describes constraints for allocating buffers of some
    // desired form.
    // |token_peer| is one endpoint of an eventpair which forms an association
    // between this request and calls to |BindSharedCollection()|.
    //
    // In the first phase, one client acts as a coordinator.  The coordinator
    // creates an event pair and designates one endpoint as the *token* and
    // the other endpoint as the *token peer*. The coordinator then calls
    // |AllocateSharedCollection()|, passing the buffer request and the token
    // peer’s handle.  It also sends a token to each client which requires
    // access to the buffer, duplicating the token’s handle if necessary.
    //
    // In the second phase, each client which received a token calls
    // |BindSharedCollection()|, passing their usages and the token.
    // As the buffer manager handles each request, it retrieves the token’s
    // kernel object id (KOID) and adds it to a list to be matched up with
    // token peers from prior or subsequent calls to
    // |AllocateSharedCollection()|.  Once matched, the token is closed
    // and the client’s corresponding usages are associated with the
    // token peer.
    //
    // This method returns once all tokens corresponding to the |token_peer|
    // are closed and the allocation completes successfully, or an error
    // occurs.
    //
    // Returns |ZX_OK| once all of the collection’s tokens have been
    // closed and buffer allocation has completed successfully.
    // Returns |ZX_ERR_ACCESS_DENIED| if the caller is not permitted to
    // obtain the buffers it requested.
    // Returns |ZX_ERR_INVALID_ARGS| if the request is malformed.
    // Returns |ZX_ERR_NOT_SUPPORTED| if request is valid but cannot be
    // satisfied, perhaps due to hardware limitations.
    2: AllocateSharedCollection(uint32 buffer_count,
                                BufferSpec spec,
                                handle<eventpair> token_peer)
           -> (zx.status status);

    // Enlists a client into a shared collection of buffers, taking into
    // account how the client intends to use the buffers.
    //
    // |usage| describes how the client intends to access the buffers.
    // |token| is the other endpoint of an eventpair passed to
    // |AllocateSharedCollection()|.
    // |collection| provides access to the allocated buffers.
    //
    // This method returns once all other tokens for the collection are
    // closed and the allocation completes successfully, or an error occurs.
    //
    // Returns |ZX_OK| once all of the collection’s tokens have been closed
    // and buffer allocation has completed successfully.
    // Returns |ZX_ERR_ACCESS_DENIED| if the caller is not permitted to
    // obtain the buffers it requested.
    // Returns |ZX_ERR_INVALID_ARGS| if the request is malformed.
    // Returns |ZX_ERR_NOT_SUPPORTED| if request is valid but cannot be
    // satisfied, perhaps due to hardware limitations.
    3: BindSharedCollection(BufferUsage usage, handle<eventpair> token)
           -> (zx.status status, BufferCollectionInfo collection);
};