1/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
2/* This Source Code Form is subject to the terms of the Mozilla Public
3 * License, v. 2.0. If a copy of the MPL was not distributed with this
4 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
5
6/*
7** prshma.h -- NSPR Anonymous Shared Memory
8**
9** NSPR provides an anonymous shared memory based on NSPR's PRFileMap
10** type. The anonymous file-mapped shared memory provides an inheritable
11** shared memory, as in: the child process inherits the shared memory.
12** Compare the file-mapped anonymous shared memory to to a named shared
13** memory described in prshm.h. The intent is to provide a shared
14** memory that is accessable only by parent and child processes. ...
15** It's a security thing.
16**
17** Depending on the underlying platform, the file-mapped shared memory
18** may be backed by a file. ... surprise! ... On some platforms, no
19** real file backs the shared memory. On platforms where the shared
20** memory is backed by a file, the file's name in the filesystem is
21** visible to other processes for only the duration of the creation of
22** the file, hopefully a very short time. This restricts processess
23** that do not inherit the shared memory from opening the file and
24** reading or writing its contents. Further, when all processes
25** using an anonymous shared memory terminate, the backing file is
26** deleted. ... If you are not paranoid, you're not paying attention.
27**
28** The file-mapped shared memory requires a protocol for the parent
29** process and child process to share the memory. NSPR provides two
30** protocols. Use one or the other; don't mix and match.
31**
32** In the first protocol, the job of passing the inheritable shared
33** memory is done via helper-functions with PR_CreateProcess(). In the
34** second protocol, the parent process is responsible for creating the
35** child process; the parent and child are mutually responsible for
36** passing a FileMap string. NSPR provides helper functions for
37** extracting data from the PRFileMap object. ... See the examples
38** below.
39**
40** Both sides should adhere strictly to the protocol for proper
41** operation. The pseudo-code below shows the use of a file-mapped
42** shared memory by a parent and child processes. In the examples, the
43** server creates the file-mapped shared memory, the client attaches to
44** it.
45**
46** First protocol.
47** Server:
48**
49** fm = PR_OpenAnonFileMap(dirName, size, FilemapProt);
50** addr = PR_MemMap(fm);
51** attr = PR_NewProcessAttr();
52** PR_ProcessAttrSetInheritableFileMap( attr, fm, shmname );
53** PR_CreateProcess(Client);
54** PR_DestroyProcessAttr(attr);
55** ... yadda ...
56** PR_MemUnmap( addr );
57** PR_CloseFileMap(fm);
58**
59**
60** Client:
61** ... started by server via PR_CreateProcess()
62** fm = PR_GetInheritedFileMap( shmname );
63** addr = PR_MemMap(fm);
64** ... yadda ...
65** PR_MemUnmap(addr);
66** PR_CloseFileMap(fm);
67**
68**
69** Second Protocol:
70** Server:
71**
72** fm = PR_OpenAnonFileMap(dirName, size, FilemapProt);
73** fmstring = PR_ExportFileMapAsString( fm );
74** addr = PR_MemMap(fm);
75** ... application specific technique to pass fmstring to child
76** ... yadda ... Server uses his own magic to create child
77** PR_MemUnmap( addr );
78** PR_CloseFileMap(fm);
79**
80**
81** Client:
82** ... started by server via his own magic
83** ... application specific technique to find fmstring from parent
84** fm = PR_ImportFileMapFromString( fmstring )
85** addr = PR_MemMap(fm);
86** ... yadda ...
87** PR_MemUnmap(addr);
88** PR_CloseFileMap(fm);
89**
90**
91** lth. 2-Jul-1999.
92**
93** Note: The second protocol was requested by NelsonB (7/1999); this is
94** to accomodate servers which already create their own child processes
95** using platform native methods.
96**
97*/
98
99#ifndef prshma_h___
100#define prshma_h___
101
102#include "prtypes.h"
103#include "prio.h"
104#include "prproces.h"
105
106PR_BEGIN_EXTERN_C
107
108/*
109** PR_OpenAnonFileMap() -- Creates an anonymous file-mapped shared memory
110**
111** Description:
112** PR_OpenAnonFileMap() creates an anonymous shared memory. If the
113** shared memory already exists, a handle is returned to that shared
114** memory object.
115**
116** On Unix platforms, PR_OpenAnonFileMap() uses 'dirName' as a
117** directory name, without the trailing '/', to contain the anonymous
118** file. A filename is generated for the name.
119**
120** On Windows platforms, dirName is ignored.
121**
122** Inputs:
123** dirName -- A directory name to contain the anonymous file.
124** size -- The size of the shared memory
125** prot -- How the shared memory is mapped. See prio.h
126**
127** Outputs:
128** PRFileMap *
129**
130** Returns:
131** Pointer to PRFileMap or NULL on error.
132**
133*/
134NSPR_API( PRFileMap *)
135PR_OpenAnonFileMap(
136 const char *dirName,
137 PRSize size,
138 PRFileMapProtect prot
139);
140
141/*
142** PR_ProcessAttrSetInheritableFileMap() -- Prepare FileMap for export
143** to my children processes via PR_CreateProcess()
144**
145** Description:
146** PR_ProcessAttrSetInheritableFileMap() connects the PRFileMap to
147** PRProcessAttr with shmname. A subsequent call to PR_CreateProcess()
148** makes the PRFileMap importable by the child process.
149**
150** Inputs:
151** attr -- PRProcessAttr, used to pass data to PR_CreateProcess()
152** fm -- PRFileMap structure to be passed to the child process
153** shmname -- The name for the PRFileMap; used by child.
154**
155** Outputs:
156** PRFileMap *
157**
158** Returns:
159** PRStatus
160**
161*/
162NSPR_API(PRStatus)
163PR_ProcessAttrSetInheritableFileMap(
164 PRProcessAttr *attr,
165 PRFileMap *fm,
166 const char *shmname
167);
168
169/*
170** PR_GetInheritedFileMap() -- Import a PRFileMap previously exported
171** by my parent process via PR_CreateProcess()
172**
173** Description:
174** PR_GetInheritedFileMap() retrieves a PRFileMap object exported from
175** its parent process via PR_CreateProcess().
176**
177** Inputs:
178** shmname -- The name provided to PR_ProcessAttrSetInheritableFileMap()
179**
180** Outputs:
181** PRFileMap *
182**
183** Returns:
184** PRFileMap pointer or NULL.
185**
186*/
187NSPR_API( PRFileMap *)
188PR_GetInheritedFileMap(
189 const char *shmname
190);
191
192/*
193** PR_ExportFileMapAsString() -- Creates a string identifying a PRFileMap
194**
195** Description:
196** Creates an identifier, as a string, from a PRFileMap object
197** previously created with PR_OpenAnonFileMap().
198**
199** Inputs:
200** fm -- PRFileMap pointer to be represented as a string.
201** bufsize -- sizeof(buf)
202** buf -- a buffer of length PR_FILEMAP_STRING_BUFSIZE
203**
204** Outputs:
205** buf contains the stringized PRFileMap identifier
206**
207** Returns:
208** PRStatus
209**
210*/
211NSPR_API( PRStatus )
212PR_ExportFileMapAsString(
213 PRFileMap *fm,
214 PRSize bufsize,
215 char *buf
216);
217#define PR_FILEMAP_STRING_BUFSIZE 128
218
219/*
220** PR_ImportFileMapFromString() -- Creates a PRFileMap from the identifying string
221**
222** Description:
223** PR_ImportFileMapFromString() creates a PRFileMap object from a
224** string previously created by PR_ExportFileMapAsString().
225**
226** Inputs:
227** fmstring -- string created by PR_ExportFileMapAsString()
228**
229** Returns:
230** PRFileMap pointer or NULL.
231**
232*/
233NSPR_API( PRFileMap * )
234PR_ImportFileMapFromString(
235 const char *fmstring
236);
237
238PR_END_EXTERN_C
239#endif /* prshma_h___ */
240

source code of include/nspr/prshma.h