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nameservice

NAME

NaClNameServiceGetRoot, NaClNameServiceChannel, NaClNameServiceResolve -- look up names in namespaces

SYNOPSIS

#include <stdint.h>
#include <fcntl.h>
#include <nacl/nameservice.h>

int32_t NaClNameServiceGetRoot(void);

void NaClNameServiceClose(int32_t service);

int32_t NaClNameServiceChannel(int32_t service);

void NaClNameServiceChannelClose(int32_t channel);

int32_t NaClNameServiceResolve(int32_t channel, char const *name, int32_t flags, int32_t mode);

size_t NaClNameServiceEnumerate(int32_t channel, char *buffer, size_t nbytes);

void NaClNameServiceChannelAsyncThread(int32_t channel);

int32_t NaClNameServiceResolveAsync(int32_t channel, char const *name, int32_t flags, int32_t mode, void (*callback)(void *state, int32_t desc, int32_t errno), void *state);

int32_t NaClNameServiceEnumerateAsync(int32_t channel, char *buffer, size_t nbytes, void (*callback)(void *state, size_t written), void *state);


DESCRIPTION

The name service interface provides a general mechanism to resolve names, mapping a NUL-terminated character string to an I/O descriptor.  Resolution may result in descriptors that represent files, name resolvers for lower-level namespaces, and, in the future, device interfaces such as video cameras or joysticks.  Initial namespaces that can be reached from the "root" namespaces are manifest files, WebFS persistent files, WebFS temporary files, and files included with the standard Native Client runtime.

NaClNameServiceGetRoot() returns a "root" name service which every Native Client module is created with. This name service identity is used to create name service channels using which name resolution can occur, using NaClNameServiceChannel().  Each Native Client module may create multiple name service channels, e.g., one per thread or to form a channel pool that grows as needed.  Each channel may be used for only one synchronous resolution operation at a time, and it is up to the Native Client module to ensure that this holds.  

As an alternative to using the synchronous API, NaClNameServiceResolveAsync may be used instead.  Before NaClNameServiceResolveAsync is used, the caller must spawn a thread and invoke NaClNameServiceChannelAsyncThread, which will only return when the channel is closed.  Here, the name service will invoke callback with the result desc -- which, on an error, will be -1, so the callback is guaranteed to be called exactly once -- once a result is available.  The callback/state functor will be invoked on a separate thread, and it is the responsibility of the NaCl module provided callback functor to process the result in a thread-safe manner.  Multiple NaClNameServiceResolveAsync may be invoked on the same channel.  However, the maximum number of NaClNameServiceResolveAsync operations actually allowed in flight is not specified, and the order of callbacks may occur in any order.  If the callback is invoked with the desc argument equal to -1, the errno argument will have a meaningful value.  If the maximum number of in-flight asynchronous name resolutions is exceeded, NaClNameServiceResolveAsync returns -1, and the caller may retry later, e.g., when a callback is invoked; otherwise NaClNameServiceResolveAsync returns 0 to indicate that the callback will fire, or may have fired.

The name, flags, and mode arguments for NaClNameServiceResolve and NaClNameServiceResolveAsync are essentially that of the familiar POSIX open(2) call, with the following differences:  flags may contain, instead of the usual O_RDONLY, O_RDWR, etc, values defined in fcntl.h, O_NAMESERVICE.  When resolving a name with O_NAMESERVICE, the mode argument is ignored.  If the resolution succeeds, the return value is a name service, which may in turn be used with NaClNameServiceChannel.  If the resolution fails, NaClNameServiceResolve returns -1 and the thread-local variable errno is set to indicate the reason for failure.

To enumerate all names at a name service, use NaClNameServiceEnumerate or NaClNameServiceEnumerateAsync.  The supplied buffer is overwritten with at most nbytes of NUL-terminate string names, and the actual number of bytes written is returned, in the case of NaClNameServiceEnumerate; or is supplied as the written input argument of the completion callback functor callback/state, in the case of NaClNameServiceEnumerateAsync.  NB: If written < nbytes, then all names in the namespace were returned.  Some name services, e.g., those associated with file systems, may permit the opening of directories as name services.

All I/O operations using I/O descriptors returned by name services will cause the caller to block until the operation succeeds, unless the NaCl thread synchronous I/O restriction is in force; in this case, the I/O restricted thread(s) will not be able to perform I/O operations unless explicitly enabled:  such operations will result in EWOULDBLOCK

Do not use both the asynchronous and synchronous resolution interfaces, even in a temporally disjoint manner.

EXAMPLES

int32_t root_nameservice = NaClNameServiceGetRoot();
int32_t root_ns_channel = NaClNameServiceChannel(root_nameservice);
int32_t web_fs_nameservice = NaClNameServiceResolve(root_ns_channel, "WebFsPersistentStore", O_NAMESERVICE, 0);
int32_t manifest_nameservice = NaClNameServiceResolve(root_ns_channel, "ManifestFiles", O_NAMESERVICE, 0);
int32_t fd = NaClNameServiceResolve(manifest_nameservice, "libsdl.so", O_RDONLY, 0);

void *ResolverThread(void *state) {
  NaClNameServiceAsyncThread((int32_t) (intptr_t) state);
  return NULL;
}

void ResolverCallback(void *state, int32_t desc, int32_t errno) {
   /* grab a lock, save desc somewhere, and signal a condvar */
  struct ResolverCallbackState *info = (struct ResolverCallbackState *) state;
  pthread_mutex_lock(&info->mu);
  info->desc = desc; info->errno = errno;
  pthread_cond_broadcast(&info->cv);
  pthread_mutex_unlock(&info->mu);
}

pthread_t tid;
struct ResolverCallbackState *info = ...;
pthread_create(&tid, (pthread_attr_t) NULL, ResolverThread, web_fs_nameservice);
if (0 != NaClNameServiceResolveAsync(web_fs_nameservice, "/Nexuiz/SavedGame", O_RDWR, 0, ResolverCallback, info)) {
  /* failed */
}

SEE ALSO

open, close, read, write, fstat, iorestrict

BUGS

stat-like call is missing; TBD.
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