duality.ps.ps

国外开发的著名分布式操作系统mach的有关代码文章

(5)SH
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(is known to the kernel at system initialization)
225 W( time)226 W
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(, in a)226 W
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(pager_create)SH
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(call. This)
702 W( call is similar in form to)226 W
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(pager_init)SH
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(; however, it cannot be made on the memory object port itself, but on a port provided by the default pager.)SH
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(Since these kernel-created objects have no initial memory, the default pager may not have data to)
149 W( provide in)148 W
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(response to a request.  In this case, it must perform a)4 W
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(pager_data_unavailable)SH
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(call to indicate that)
4 W( the page should be)5 W
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(6)SH
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(zero-filled)SH
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(.)SH
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(4. Using Memory Objects)SH
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(This section briefly describes two sample data managers)
84 W( and their applications.  The first is a filesystem with a)83 W
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(read/copy-on-write interface, which uses the minimal subset of the memory management interface.  The second)
78 W( is)79 W
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(an excerpt from the operation of a consistent network shared memory service.)SH
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(4.1. A Minimal Filesystem)SH
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(An example of a service which minimally uses the Mach external interface is a filesystem server which provides)46 W
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(read-whole-file/write-whole-file functionality.  Although it is simple, this style of interface has been used in)
63 W( actual)64 W
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(servers [12, 19] and should be considered a serious example.)SH
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(An application might use this filesystem as follows:)SH
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(4)SH
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(The same mechanism is used for)SH
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(shadow objects)SH
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(that contain changes to copy-on-write data.)SH
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(5)SH
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(The default pager will be described in more detail in a later section.)SH
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(6)SH
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(When shadowing, the data is instead copied from the original.)SH
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(9)SH
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(char *file_data;)SH
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(int i, file_size;)SH
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(extern float rand\050\051;)
SH( /*)
1620 W( random in [0,1\051 */)SH
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(/* Read the file -- ignore errors */)SH
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(fs_read_file\050"filename", &file_data, file_size\051;)SH
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(/* Randomly change contents */)SH
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(for \050i = 0; i < file_size; i++\051)SH
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(file_data[\050int\051\050file_size*rand\050\051\051]++;)SH
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(/* Write back some results -- ignore errors */)SH
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(fs_write_file\050"filename", file_data, file_size/2\051;)SH
9360 21034 MT
(/* Throw away working copy */)SH
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(vm_deallocate\050task_self\050\051, file_data, file_size\051;)SH
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(Note that the)213 W
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(fs_read_file)SH
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(call returns new virtual memory as a result.  This memory is copy-on-write in)
213 W( the)212 W
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(application's address space; other applications will consistently see)
188 W( the original file contents while the random)189 W
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(changes are being made.  The application must explicitly store back its changes.)SH
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(To process the)182 W
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(fs_read_file)SH
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(request, the filesystem server)
182 W( creates a memory object and maps it into)181 W
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(its own)181 W
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(address space.  It then returns that memory region)
74 W( through the IPC mechanism so that it will be mapped copy-on-)75 W
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(7)SH
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(write in the client's address space.)SH
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(return_t fs_read_file\050name, data, size\051)SH
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(string_t name;)SH
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(char **data;)SH
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(int *size;)SH
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({)SH
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(port_t new_object;)2160 W
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(/* Allocate a memory object \050a port\051, */)SH
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(/* and accept request */)SH
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(port_allocate\050task_self\050\051, &new_object\051;)SH
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(port_enable\050task_self\050\051, new_object\051;)SH
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(/* Perform file lookup, find current file size,*/)SH
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(/* record association of file to new_object */)SH
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(...)SH
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(/* Map the memory object into our address space*/)SH
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(vm_allocate_with_pager\050task_self\050\051, data, *size,)SH
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(TRUE, new_object, 0\051;)SH
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(return\050success\051;)SH
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(})SH
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(When the)95 W
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(vm_allocate_with_pager)SH
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(call is performed, the kernel will issue)
95 W( a)96 W
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(pager_init)SH
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(call. The)
442 W( filesystem must)96 W
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(receive this message at some time, and should record the pager request port contained therein.)SH
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(When the application)
53 W( first uses a page of the data, it generates a page fault.  To fill that fault, the kernel issues a)52 W
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(pager_data_request)SH
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(for that page.  To fulfill this request, the data)
96 W( manager responds with a)97 W
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(pager_data_provided)SH
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(call.)SH
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(7)SH
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(If the client were)
64 W( to map the memory object into its address space using)63 W
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(vm_allocate_with_pager)SH
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(, the client would not see a copy-on-write)63 W
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(version of the data, but would have read/write access to the memory object.)SH
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(10)SH
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(void pager_data_request\050memory_object, pager_request,)SH
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(offset, size, access\051)SH
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(port_t memory_object;)SH
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(port_t pager_request;)SH
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(vm_offset_t offset;)SH
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(vm_size_t size;)SH
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(vm_prot_t access;)SH
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({)SH
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(char *data;)SH
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(/* Allocate disk buffer */)SH
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(vm_allocate\050task_self\050\051, &data, size\051;)SH
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(/* Lookup memory_object; find actual disk data*/)SH
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(disk_read\050disk_address\050memory_object, offset\051,)SH
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(data, size\051;)SH
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(/* Return the data with no locking */)SH
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(pager_data_provided\050pager_request, offset, data,)SH
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(size, VM_PROT_NONE\051;)SH
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(/* Deallocate disk buffer */)SH
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(vm_deallocate\050task_self\050\051, data, size\051;)SH
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(})SH
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(The filesystem will never receive any)131 W
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(pager_data_write)SH
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(or)SH
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(pager_data_unlock)SH
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(requests. After)
510 W( the application)130 W
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(deallocates its memory copy)
52 W( of the file, the filesystem will receive a port death message for the pager request port.)53 W
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(It can then release its data structures and resources for this file.)SH
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(void port_death\050request_port\051)SH
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(port_t request_port;)SH
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({)SH
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(port_t memory_object;)SH
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(char *data;)SH
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(int size;)SH
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(/* Find the associated memory object */)SH
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(lookup_by_request_port\050request_port,)SH
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(&memory_object, &data, &size\051;)SH
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(/* Release resources */)SH
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(port_deallocate\050task_self\050\051, memory_object\051;)SH
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(vm_deallocate\050task_self\050\051, data, size\051;)SH
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(})SH
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(4.2. Consistent Network Shared Memory Excerpt)SH
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(In this subsection)
99 W( we describe how the memory management interface might be used to implement a region of)98 W
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(shared memory between two clients on different hosts.)SH
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(In order to use the shared memory region, a client must first contact a data manager which provides)
173 W( shared)174 W
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(memory service.  In our example, the first client has made a request for a shared memory region not in use by any)57 W
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(other client.  The shared)
87 W( memory server creates a memory object \050)88 W
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(i.e.)SH
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(, allocates a port\051 to refer to this region and)88 W
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(returns that memory object, X, to the first client.)SH
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(8)SH
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(The second)
81 W( client, running on a different host, later makes a request for the same shared memory region)80 W
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(. The)410 W
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(shared memory server finds the memory object, X, and returns it to the second client.)SH
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(8)SH
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(How it specifies that region \050e.g., by name or by use of another capability\051 is not important to the example.)SH
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(11)SH
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(Each client maps the memory object X into its address space, using)123 W
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(vm_allocate_with_pager)SH
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(. As)
498 W( each kernel)124 W
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(processes that call, it makes a)56 W
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19617 XM
(pager_init)SH
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(call to the memory object X. The shared memory)
56 W( server records each use)55 W
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(of X, and the pager request and name ports for those uses.  Note that the Mach kernel does not await a reply from)63 W
7200 12017 MT
(the shared memory server, but does perform the)39 W
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(pager_init)SH
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(call before allowing the)39 W
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(vm_allocate_with_pager)SH
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(call to)39 W
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(complete. Also)
346 W( note that while there)
48 W( is only one memory object port \050X\051, there are distinct request and name ports)49 W
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(for each kernel.)
39 W( In)
326 W( this example, the shared memory server may be located on either of the clients' hosts, or on yet)38 W
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(another host.)SH
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(In the second frame, each)
26 W( client takes a read fault on the same page of the shared memory region. The same page)27 W
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(may be mapped to different)
21 W( addresses in the two clients.  Each kernel makes a)20 W
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(pager_data_request)SH
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(on X, specifying)20 W
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(its own pager request port for X.)
158 W( The shared memory server replies using the)159 W
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(pager_data_provided)SH
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(call on the)159 W
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(appropriate request port.  Since the request only requires read access, the)
27 W( shared memory server applies a write lock)26 W
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(9)SH
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(on the data as it is returned)21 W
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(. The)
290 W( shared memory server must also record all of the uses \050i.e. pager request ports\051 of)20 W
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(this page.)SH
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(In the final frame, one client attempts to write)