Attach a path to the pathname space
#include <sys/iofunc.h>
#include <sys/resmgr.h>
#include <sys/dispatch.h>
int resmgr_attach (
dispatch_t *dpp,
resmgr_attr_t *attr,
const char *path,
enum _file_type file_type,
unsigned flags,
const resmgr_connect_funcs_t *connect_funcs,
const resmgr_io_funcs_t *io_funcs,
RESMGR_HANDLE_T *handle );
For more information, see “The flags argument,” below.
libc
Use the -l c option to qcc to link against this library. This library is usually included automatically.
The resmgr_attach() function puts the path into the general pathname space and binds requests on this path to the dispatch handle dpp. You usually provide an absolute path; if you provide a path that doesn't start with a slash, it's considered to be relative to the current working directory. If path is NULL, resmgr_attach() just sets up the dispatch structure.
For more information, see procmgr_ability().
Most of the above file types are used for special services that have their own open function associated with them. For example, the mqueue manager specifies file_type as _FTYPE_MQUEUE, and mq_open() requests a pathname match of the same type.
Specify _FTYPE_ANY for normal filesystems and simple devices, such as serial ports, that don't have their own special open type, or if your resource manager can handle the type of service or act as a redirection node to a manager that does. Most resource managers are of this type.
Your resource manager won't receive messages from an open of an inappropriate type. The following table shows the different open function types and the types of pathnames they'll match.
| Function: | file_type: | Matches pathname of type: |
|---|---|---|
| mq_open() | _FTYPE_MQ | _FTYPE_ANY or _FTYPE_MQ |
| mq_open() | _FTYPE_MQUEUE | _FTYPE_ANY or _FTYPE_MQUEUE |
| open() | _FTYPE_ANY | All types |
| pipe() | _FTYPE_PIPE | _FTYPE_ANY or _FTYPE_PIPE |
| sem_open() | _FTYPE_SEM | _FTYPE_ANY or _FTYPE_SEM |
| shm_open() | _FTYPE_SHMEM | _FTYPE_ANY or _FTYPE_SHMEM |
| socket() | _FTYPE_SOCKET | _FTYPE_ANY or _FTYPE_SOCKET |
The generic open() can be used to open a pathname of any type.
If you want to use the POSIX functions, we've provided you with the POSIX layer; to fill your connect and I/O functions tables with the default handler functions supplied by the POSIX layer library, call iofunc_func_init(). You can then override the defaults placed in the structures with your own handlers.
In the most general case, the last argument, handle is an arbitrary structure that you wish to have associated with the pathname you're attaching. Practically, however, we recommend that it contain the POSIX layer's well defined attributes structure, iofunc_attr_t, because this lets you use the POSIX-layer default library. You can extend the data that's contained in the attributes structure to contain any device-specific data that you may require. This is commonly done, and is described in the Extending the POSIX-Layer Data Structures chapter of Writing a Resource Manager.
In order to use the POSIX layer default library, the attributes structure must be bound into the Open Control Block, and you must use the POSIX layer's iofunc_ocb_t OCB. This is described in the documentation for resmgr_open_bind(), as well as in the above reference.
resmgr_attr_t structure
You can specify attributes such as the maximum message size, number of parts (number of IOVs in context), and flags in the attr structure. The resmgr_attr_t structure looks like this:
typedef struct _resmgr_attr {
unsigned flags;
unsigned nparts_max;
size_t msg_max_size;
int (*other_func) ( resmgr_context_t *, void *msg );
unsigned reserved[4];
} resmgr_attr_t;
The members include:
The flags argument
The flags argument to resmgr_attach() specifies additional information to control the pathname resolution.
The flags (defined in <sys/resmgr.h>) include at least the following bits:
| Attached path | Opened path | _RESMGR_FLAG_DIR set | _RESMGR_FLAG_DIR clear |
|---|---|---|---|
| /a/b | /a/b | Match "" | Match "" |
| /a/b | /a/b/c | Match c | No match |
| /a/b | /a/b/c/d | Match c/d | No match |
| /a/b | /a/bc | No match | No match |
You can't attach a directory pathname that contains, as a subset, an existing file pathname. Likewise, you can't attach a file pathname that's a subset of an existing directory pathname.
| Existing path | New path | New path allowed? |
|---|---|---|
| Directory /a/b | Directory /a | Yes |
| Directory /a/b | Directory /a/b/c | Yes |
| File /a/b | Directory /a | Yes |
| File /a/b | Directory /a/b/c | No; the directory is beneath a file |
| Directory /a/b | File /a | No; the directory is beneath a file |
| Directory /a/b | File /a/b/c | Yes |
| File /a/b | File /a | Yes |
| File /a/b | File /a/b/c | Yes |
A unique link ID associated with this attach, or -1 on failure (errno is set).
The returned ID is needed to detach the pathname at a later time using resmgr_detach(). The ID is also passed back in the resmgr_handler() function in ctp->id.
Here's an example of a simple single-threaded resource manager:
#include <stdio.h>
#include <stddef.h>
#include <stdlib.h>
#include <sys/iofunc.h>
#include <sys/dispatch.h>
static resmgr_connect_funcs_t connect_funcs;
static resmgr_io_funcs_t io_funcs;
static iofunc_attr_t attr;
int main(int argc, char **argv)
{
dispatch_t *dpp;
resmgr_attr_t resmgr_attr;
resmgr_context_t *ctp;
int id;
/* initialize dispatch interface */
if ( (dpp = dispatch_create()) == NULL ) {
fprintf( stderr, "%s: Unable to allocate \
dispatch handle.\n", argv[0] );
return EXIT_FAILURE;
}
/* initialize resource manager attributes */
memset( &resmgr_attr, 0, sizeof resmgr_attr );
resmgr_attr.nparts_max = 1;
resmgr_attr.msg_max_size = 2048;
/* initialize functions for handling messages */
iofunc_func_init( _RESMGR_CONNECT_NFUNCS, &connect_funcs,
_RESMGR_IO_NFUNCS, &io_funcs );
/* initialize attribute structure */
iofunc_attr_init( &attr, S_IFNAM | 0666, 0, 0 );
/* attach our device name (passing in the POSIX defaults
from the iofunc_func_init and iofunc_attr_init functions)
*/
if ( (id = resmgr_attach
( dpp, &resmgr_attr, "/dev/mynull", _FTYPE_ANY, 0,
&connect_funcs, &io_funcs, &attr)) == -1 ) {
fprintf( stderr, "%s: Unable to attach name.\n", \
argv[0] );
return EXIT_FAILURE;
}
/* allocate a context structure */
ctp = resmgr_context_alloc( dpp );
/* start the resource manager message loop */
while (1) {
if ( (ctp = resmgr_block( ctp )) == NULL ) {
fprintf(stderr, "block error\n");
return EXIT_FAILURE;
}
resmgr_handler(ctp);
}
}
For more examples using the dispatch interface, see dispatch_create(), message_attach(), and thread_pool_create(). For more information on writing a resource manager, see Writing a Resource Manager
| Safety: | |
|---|---|
| Cancellation point | Yes |
| Interrupt handler | No |
| Signal handler | No |
| Thread | No |