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1 | BDSH - The Brain Dead Shell | Design Documentation |
1 | BDSH - The Brain Dead Shell | Design Documentation |
2 | -------------------------------------------------- |
2 | -------------------------------------------------- |
3 | 3 | ||
4 | Overview: |
4 | Overview: |
5 | ========= |
5 | ========= |
6 | 6 | ||
7 | BDSH was written as a drop in command line interface for HelenOS to permit |
7 | BDSH was written as a drop in command line interface for HelenOS to permit |
8 | interactive access to persistent file systems in development. BDSH was |
8 | interactive access to persistent file systems in development. BDSH was |
9 | written from scratch with a very limited userspace standard C library in |
9 | written from scratch with a very limited userspace standard C library in |
10 | mind. Much like the popular Busybox program, BDSH provides a very limited |
10 | mind. Much like the popular Busybox program, BDSH provides a very limited |
11 | shell with limited common UNIX creature comforts built in. |
11 | shell with limited common UNIX creature comforts built in. |
12 | 12 | ||
13 | Porting Busybox (and by extension ASH) would have taken much longer to |
13 | Porting Busybox (and by extension ASH) would have taken much longer to |
14 | complete, much less make stable due to stark differences between Linux and |
14 | complete, much less make stable due to stark differences between Linux and |
15 | Spartan with regards to IPC, term I/O and process creation. BDSH was written |
15 | Spartan with regards to IPC, term I/O and process creation. BDSH was written |
16 | and made stable within the space of less than 30 days. |
16 | and made stable within the space of less than 30 days. |
17 | 17 | ||
18 | BDSH will eventually evolve and be refined into the HelenOS equivalent |
18 | BDSH will eventually evolve and be refined into the HelenOS equivalent |
19 | of Busybox. While BDSH is now very intrinsic to HelenOS, its structure and |
19 | of Busybox. While BDSH is now very intrinsic to HelenOS, its structure and |
20 | use of strictly lower level functions makes it extremely easy to port. |
20 | use of strictly lower level functions makes it extremely easy to port. |
21 | 21 | ||
22 | Design: |
22 | Design: |
23 | ======= |
23 | ======= |
24 | 24 | ||
25 | BDSH is made up of three basic components: |
25 | BDSH is made up of three basic components: |
26 | 26 | ||
27 | 1. Main i/o, error handling and task management |
27 | 1. Main i/o, error handling and task management |
28 | 2. The builtin sub system |
28 | 2. The builtin sub system |
29 | 3. The module sub system |
29 | 3. The module sub system |
30 | 30 | ||
31 | The main part handles user input, reports errors, spawns external tasks and |
31 | The main part handles user input, reports errors, spawns external tasks and |
32 | provides a convenient entry point for built-in and modular commands. A simple |
32 | provides a convenient entry point for built-in and modular commands. A simple |
33 | structure, cliuser_t keeps track of the user's vitals, such as their current |
33 | structure, cliuser_t keeps track of the user's vitals, such as their current |
34 | working directory (and eventually uid, home directory, etc if they apply). |
34 | working directory (and eventually uid, home directory, etc if they apply). |
35 | 35 | ||
36 | This part defines and exposes all functions that are not intrinsic to a |
36 | This part defines and exposes all functions that are not intrinsic to a |
37 | certain built in or modular command. For instance: string handlers, |
37 | certain built in or modular command. For instance: string handlers, |
38 | module/builtin search and launch functions, error handlers and other things |
38 | module/builtin search and launch functions, error handlers and other things |
39 | can be found here. |
39 | can be found here. |
40 | 40 | ||
41 | Builtin commands are commands that must have access to cliuser_t, which is |
41 | Builtin commands are commands that must have access to cliuser_t, which is |
42 | not exposed to modular commands. For instance, the 'cd' command must update |
42 | not exposed to modular commands. For instance, the 'cd' command must update |
43 | the current working directory, which is stored in cliuser_t. As such, the |
43 | the current working directory, which is stored in cliuser_t. As such, the |
44 | entry types for builtin commands are slightly different. |
44 | entry types for builtin commands are slightly different. |
45 | 45 | ||
46 | Modular commands do not need anything more than the basic functions that are |
46 | Modular commands do not need anything more than the basic functions that are |
47 | exposed by default. They do not need to modify cliuser_t, they are just self |
47 | exposed by default. They do not need to modify cliuser_t, they are just self |
48 | contained. A modular command could very easily be made into a stand alone |
48 | contained. A modular command could very easily be made into a stand alone |
49 | program, likewise any stand alone program could easily become a modular |
49 | program, likewise any stand alone program could easily become a modular |
50 | command. |
50 | command. |
51 | 51 | ||
52 | Both modular and builtin commands share two things in common. Both must have |
52 | Both modular and builtin commands share two things in common. Both must have |
53 | two entry points, one to invoke the command and one to invoke a help display |
53 | two entry points, one to invoke the command and one to invoke a help display |
54 | for the command. Exec (main()) entry points are int * and are expected to |
54 | for the command. Exec (main()) entry points are int * and are expected to |
55 | return a value. Help entry points are void *, no return value is expected. |
55 | return a value. Help entry points are void *, no return value is expected. |
56 | 56 | ||
57 | They are typed as such (from cmds.h): |
57 | They are typed as such (from cmds.h): |
58 | 58 | ||
59 | /* Types for module command entry and help */ |
59 | /* Types for module command entry and help */ |
60 | typedef int (* mod_entry_t)(char **); |
60 | typedef int (* mod_entry_t)(char **); |
61 | typedef void (* mod_help_t)(unsigned int); |
61 | typedef void (* mod_help_t)(unsigned int); |
62 | 62 | ||
63 | /* Built-in commands need to be able to modify cliuser_t */ |
63 | /* Built-in commands need to be able to modify cliuser_t */ |
64 | typedef int (* builtin_entry_t)(char **, cliuser_t *); |
64 | typedef int (* builtin_entry_t)(char **, cliuser_t *); |
65 | typedef void (* builtin_help_t)(unsigned int); |
65 | typedef void (* builtin_help_t)(unsigned int); |
66 | 66 | ||
67 | As you can see, both modular and builtin commands expect an array of |
67 | As you can see, both modular and builtin commands expect an array of |
68 | arguments, however bulitins also expect to be pointed to cliuser_t. |
68 | arguments, however bulitins also expect to be pointed to cliuser_t. |
69 | 69 | ||
70 | Both are defined with the same simple structure: |
70 | Both are defined with the same simple structure: |
71 | 71 | ||
72 | /* Module structure */ |
72 | /* Module structure */ |
73 | typedef struct { |
73 | typedef struct { |
74 | char *name; /* Name of the command */ |
74 | char *name; /* Name of the command */ |
75 | char *desc; /* Description of the command */ |
75 | char *desc; /* Description of the command */ |
76 | mod_entry_t entry; /* Command (exec) entry function */ |
76 | mod_entry_t entry; /* Command (exec) entry function */ |
77 | mod_help_t help; /* Command (help) entry function */ |
77 | mod_help_t help; /* Command (help) entry function */ |
78 | int restricted; /* Restricts to interactive/non-interactive only */ |
78 | int restricted; /* Restricts to interactive/non-interactive only */ |
79 | } module_t; |
79 | } module_t; |
80 | 80 | ||
81 | NOTE: Builtin commands may grow in this respect, that is why they are |
81 | NOTE: Builtin commands may grow in this respect, that is why they are |
82 | defined separately. |
82 | defined separately. |
83 | 83 | ||
84 | Builtins, of course, would use the builtin_entry_t type. The name of the |
84 | Builtins, of course, would use the builtin_entry_t type. The name of the |
85 | command is used to associate user input to a possible entry point. The |
85 | command is used to associate user input to a possible entry point. The |
86 | description is a short (40 - 60 chars) summary of what the command does. Both |
86 | description is a short (40 - 60 chars) summary of what the command does. Both |
87 | entry points are then defined, and the restrict value is used to determine a |
87 | entry points are then defined, and the restrict value is used to determine a |
88 | commands availability. |
88 | commands availability. |
89 | 89 | ||
90 | Restriction levels are easy, a command is either available exclusively within |
90 | Restriction levels are easy, a command is either available exclusively within |
91 | interactive mode, exclusively within non-interactive mode or both. If you are |
91 | interactive mode, exclusively within non-interactive mode or both. If you are |
92 | looking at a prompt, you are in interactive mode. If you issue a command like |
92 | looking at a prompt, you are in interactive mode. If you issue a command like |
93 | this: |
93 | this: |
94 | 94 | ||
95 | /sbin/bdsh command [arg1] [arg2] |
95 | /sbin/bdsh command [arg1] [arg2] |
96 | 96 | ||
97 | ... you are in non interactive mode. This is done when you need to force the |
97 | ... you are in non interactive mode. This is done when you need to force the |
98 | parent shell to be the one who actually handles the command, or ensure that |
98 | parent shell to be the one who actually handles the command, or ensure that |
99 | /sbin/ls was used in lieu of the built in 'ls' when in non-interactive mode. |
99 | /sbin/ls was used in lieu of the built in 'ls' when in non-interactive mode. |
100 | 100 | ||
101 | The values are: |
101 | The values are: |
102 | 0 : Unrestricted |
102 | 0 : Unrestricted |
103 | -1 : Interactive only |
103 | -1 : Interactive only |
104 | 1 : Non-interactive only |
104 | 1 : Non-interactive only |
105 | 105 | ||
106 | A script to generate skeletal files for a new command is included, it can be |
106 | A script to generate skeletal files for a new command is included, it can be |
107 | found in cmds/mknewcmd. To generate a new modular command named 'foo', which |
107 | found in cmds/mknewcmd. To generate a new modular command named 'foo', which |
108 | should also be reachable by typing 'f00', you would issue this command: |
108 | should also be reachable by typing 'f00', you would issue this command: |
109 | 109 | ||
110 | ./mknewcmd -n foo -a f00 -t module |
110 | ./mknewcmd -n foo -a f00 -t module |
111 | 111 | ||
112 | This generates all needed files and instructs you on how to include your new |
112 | This generates all needed files and instructs you on how to include your new |
113 | command in the build and make it accessible. By default, the command will be |
113 | command in the build and make it accessible. By default, the command will be |
114 | unrestricted. Builtin commands can be created by changing 'module' to |
114 | unrestricted. Builtin commands can be created by changing 'module' to |
115 | 'builtin' |
115 | 'builtin' |
116 | 116 | ||
117 | There are more options to mknewcmd, which allow you to specify the |
117 | There are more options to mknewcmd, which allow you to specify the |
118 | description, entry point, help entry point, or restriction. By default, names |
118 | description, entry point, help entry point, or restriction. By default, names |
119 | just follow the command such as cmd_foo(), help_cmd_foo(), 'The foo command', |
119 | just follow the command such as cmd_foo(), help_cmd_foo(), 'The foo command', |
120 | etc. If you want to see the options and explanations in detail, use |
120 | etc. If you want to see the options and explanations in detail, use |
121 | ./mknewcmd --help. |
121 | ./mknewcmd --help. |
122 | 122 | ||
123 | When working with commands, keep in mind that only the main and help entry |
123 | When working with commands, keep in mind that only the main and help entry |
124 | points need to be exposed. If commands share the same functions, put them |
124 | points need to be exposed. If commands share the same functions, put them |
125 | where they are exposed to all commands, without the potential oops of those |
125 | where they are exposed to all commands, without the potential oops of those |
126 | functions going away if the command is eliminated in favor of a stand alone |
126 | functions going away if the command is eliminated in favor of a stand alone |
127 | external program. |
127 | external program. |
128 | 128 | ||
129 | The util.c file is a great place to put those types of functions. |
129 | The util.c file is a great place to put those types of functions. |
130 | 130 | ||
131 | Also, be careful with globals, option structures, etc. The compiler will |
131 | Also, be careful with globals, option structures, etc. The compiler will |
132 | generally tell you if you've made a mistake, however declaring: |
132 | generally tell you if you've made a mistake, however declaring: |
133 | 133 | ||
134 | volatile int foo |
134 | volatile int foo |
135 | 135 | ||
136 | ... in a command will allow for anything else to pick it up. Sometimes |
136 | ... in a command will allow for anything else to pick it up. Sometimes |
137 | this could be desirable .. other times not. When communicating between |
137 | this could be desirable .. other times not. When communicating between |
138 | builtins and the main system, try to use cliuser_t. The one exception |
138 | builtins and the main system, try to use cliuser_t. The one exception |
139 | for this is the cli_quit global, since everything may at some point |
139 | for this is the cli_quit global, since everything may at some point |
140 | need to check it. Modules should only communicate their return value. |
140 | need to check it. Modules should only communicate their return value. |
141 | 141 | ||
142 | Symbolic constants that everything needs should go in the config.h file, |
142 | Symbolic constants that everything needs should go in the config.h file, |
143 | however this is not the place to define shared macros. |
143 | however this is not the place to define shared macros. |
144 | 144 | ||
145 | Making a program into a module |
145 | Making a program into a module |
146 | ============================== |
146 | ============================== |
147 | 147 | ||
148 | If you have some neat program that would be useful as a modular command, |
148 | If you have some neat program that would be useful as a modular command, |
149 | converting it is not very hard. The following steps should get you through |
149 | converting it is not very hard. The following steps should get you through |
150 | the process easily (assuming your program is named 'foo'): |
150 | the process easily (assuming your program is named 'foo'): |
151 | 151 | ||
152 | 1: Use mknewcmd to generate the skeletal files. |
152 | 1: Use mknewcmd to generate the skeletal files. |
153 | 153 | ||
154 | 2: Change your "usage()" command as shown: |
154 | 2: Change your "usage()" command as shown: |
155 | -- void usage(...) |
155 | -- void usage(...) |
156 | ++ void help_cmd_foo(unsigned int level) |
156 | ++ void help_cmd_foo(unsigned int level) |
157 | 157 | ||
158 | 'level' is either 0 or 1, indicating the level of help requested. |
158 | 'level' is either 0 or 1, indicating the level of help requested. |
159 | If the help / usage function currently exits based on how it is |
159 | If the help / usage function currently exits based on how it is |
160 | called, you'll need to change it. |
160 | called, you'll need to change it. |
161 | 161 | ||
162 | 3: Change the programs "main()" as shown: |
162 | 3: Change the programs "main()" as shown: |
163 | -- int main(int argc, char **argv) |
163 | -- int main(int argc, char **argv) |
164 | ++ int cmd_foo(char **argv) |
164 | ++ int cmd_foo(char **argv) |
165 | -- return 1; |
165 | -- return 1; |
166 | ++ return CMD_FAILURE; |
166 | ++ return CMD_FAILURE; |
167 | -- return 0; |
167 | -- return 0; |
168 | ++ return CMD_SUCCESS; |
168 | ++ return CMD_SUCCESS; |
169 | 169 | ||
170 | NOTE: If main is void, you'll need to change it and ensure that its |
170 | NOTE: If main is void, you'll need to change it and ensure that its |
171 | expecting an array of arguments, even if they'll never be read or |
171 | expecting an array of arguments, even if they'll never be read or |
172 | used. I.e.: |
172 | used. I.e.: |
173 | 173 | ||
174 | -- void main(void) |
174 | -- void main(void) |
175 | ++ int cmd_foo(char **argv) |
175 | ++ int cmd_foo(char **argv) |
176 | 176 | ||
177 | 4: Don't expose more than the entry and help points: |
177 | 4: Don't expose more than the entry and help points: |
178 | -- void my_function(int n) |
178 | -- void my_function(int n) |
179 | ++ static void my_function(int n) |
179 | ++ static void my_function(int n) |
180 | 180 | ||
181 | 5: Copy/paste to the stub generated by mknewcmd then add your files to the |
181 | 5: Copy/paste to the stub generated by mknewcmd then add your files to the |
182 | Makefile. Be sure to add any directories that you made to the SUBDIRS so |
182 | Makefile. Be sure to add any directories that you made to the SUBDIRS so |
183 | that a 'make clean' will clean them. |
183 | that a 'make clean' will clean them. |
184 | 184 | ||
185 | Provided that all functions that your calling are available in the |
185 | Provided that all functions that your calling are available in the |
186 | userspace C library, your program should compile just fine and appear |
186 | userspace C library, your program should compile just fine and appear |
187 | as a modular command. |
187 | as a modular command. |
188 | 188 | ||
189 | Overcoming userspace libc obstacles |
189 | Overcoming userspace libc obstacles |
190 | =================================== |
190 | =================================== |
191 | 191 | ||
192 | A quick glance through the util.c file will reveal functions like |
192 | A quick glance through the util.c file will reveal functions like |
193 | cli_strdup(), cli_strtok(), cli_strtok_r() and more. Those are functions |
193 | cli_strdup(), cli_strtok(), cli_strtok_r() and more. Those are functions |
194 | that were missing from userspace libc when BDSH was born. Later, after |
194 | that were missing from userspace libc when BDSH was born. Later, after |
195 | porting what was needed from FBSD/NBSD, the real functions appeared in |
195 | porting what was needed from FBSD/NBSD, the real functions appeared in |
196 | the userspace libc after being tested in their cli_* implementations. |
196 | the userspace libc after being tested in their cli_* implementations. |
197 | 197 | ||
198 | Those functions remain because they guarantee that bdsh will work even |
198 | Those functions remain because they guarantee that bdsh will work even |
199 | on systems that lack them. Additionally, more BDSH specific stuff can |
199 | on systems that lack them. Additionally, more BDSH specific stuff can |
200 | go into them, such as error handling and reporting when malloc() fails. |
200 | go into them, such as error handling and reporting when malloc() fails. |
201 | 201 | ||
202 | You will also notice that FILE, fopen() (and all friends), ato*() and |
202 | You will also notice that FILE, fopen() (and all friends), ato*() and |
203 | other common things might be missing. The HelenOS userspace C library is |
203 | other common things might be missing. The HelenOS userspace C library is |
204 | still very young, you are sure to run into something that you want/need |
204 | still very young, you are sure to run into something that you want/need |
205 | which is missing. |
205 | which is missing. |
206 | 206 | ||
207 | When that happens, you have three options: |
207 | When that happens, you have three options: |
208 | 208 | ||
209 | 1 - Implement it internally in util.c , when its tested and stable send a |
209 | 1 - Implement it internally in util.c , when its tested and stable send a |
210 | patch to HelenOS asking for your function to be included in libc. This is |
210 | patch to HelenOS asking for your function to be included in libc. This is |
211 | the best option, as you not only improve BDSH .. but HelenOS as a whole. |
211 | the best option, as you not only improve BDSH .. but HelenOS as a whole. |
212 | 212 | ||
213 | 2 - Work around it. Not everyone can implement / port fopen() and all of |
213 | 2 - Work around it. Not everyone can implement / port fopen() and all of |
214 | its friends. Make open(), read(), write() (etc) work if at all possible. |
214 | its friends. Make open(), read(), write() (etc) work if at all possible. |
215 | 215 | ||
216 | 3 - Send an e-mail to the HelenOS development mailing list. Explain why you |
216 | 3 - Send an e-mail to the HelenOS development mailing list. Explain why you |
217 | need the function and what its absence is holding up. |
217 | need the function and what its absence is holding up. |
218 | 218 | ||
219 | If what you need is part of a library that is typically a shared object, try |
219 | If what you need is part of a library that is typically a shared object, try |
220 | to implement a 'mini' version of it. Currently, all userspace applications |
220 | to implement a 'mini' version of it. Currently, all userspace applications |
221 | are statically linked. Giving up creature comforts for size while avoiding |
221 | are statically linked. Giving up creature comforts for size while avoiding |
222 | temporary 'band aids' is never frowned upon. |
222 | temporary 'band aids' is never frowned upon. |
223 | 223 | ||
224 | Most of all, don't get discouraged .. ask for some help prior to giving up |
224 | Most of all, don't get discouraged .. ask for some help prior to giving up |
225 | if you just can't accomplish something with the limited means provided. |
225 | if you just can't accomplish something with the limited means provided. |
226 | 226 | ||
227 | Contributing |
227 | Contributing |
228 | ============ |
228 | ============ |
229 | 229 | ||
230 | I will take any well written patch that sanely improves or expands BDSH. Send |
230 | I will take any well written patch that sanely improves or expands BDSH. Send |
231 | me a patch against the trunk revision, or, if you like a Mercurial repository |
231 | me a patch against the trunk revision, or, if you like a Mercurial repository |
232 | is also maintained at http://echoreply.us/hg/bdsh.hg and kept in sync with |
232 | is also maintained at http://echoreply.us/hg/bdsh.hg and kept in sync with |
233 | the trunk. |
233 | the trunk. |
234 | 234 | ||
235 | Please be sure to follow the simple coding standards outlined at |
235 | Please be sure to follow the simple coding standards outlined at |
236 | http://www.helenos.eu/cstyle (mostly just regarding formatting), test your |
236 | http://www.helenos.eu/cstyle (mostly just regarding formatting), test your |
237 | changes and make sure your patch applies cleanly against the latest revision. |
237 | changes and make sure your patch applies cleanly against the latest revision. |
238 | 238 | ||
239 | All patches submitted must be your original code, or a derivative work of |
239 | All patches submitted must be your original code, or a derivative work of |
240 | something licensed under the same 3 clause BSD license as BDSH. See LICENSE |
240 | something licensed under the same 3 clause BSD license as BDSH. See LICENSE |
241 | for more information. |
241 | for more information. |
242 | 242 | ||
243 | When sending patches, you agree that your work will be published under the |
243 | When sending patches, you agree that your work will be published under the |
244 | same 3 clause BSD license as BDSH itself. Failure to ensure that anything |
244 | same 3 clause BSD license as BDSH itself. Failure to ensure that anything |
245 | you used is not under the same or less restrictive license could cause major |
245 | you used is not under the same or less restrictive license could cause major |
246 | issues for BDSH in the future .. please be sure. Also, please don't forget |
246 | issues for BDSH in the future .. please be sure. Also, please don't forget |
247 | to add yourself in the AUTHORS file, as I am horrible about keeping such |
247 | to add yourself in the AUTHORS file, as I am horrible about keeping such |
248 | things up to date. |
248 | things up to date. |
249 | 249 | ||
250 | 250 | ||
251 | 251 | ||
252 | 252 | ||
253 | 253 |