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diff --git a/doc/info/bus.texinfo b/doc/info/bus.texinfo index ab3c276..2a24cc1 100644 --- a/doc/info/bus.texinfo +++ b/doc/info/bus.texinfo @@ -71,6 +71,7 @@ Texts. A copy of the license is included in the section entitled * Overview:: Brief overview of @command{bus}. * Standard:: How to use @command{bus} properly. * Invoking:: Executing @command{bus}. +* Interface:: Using @command{libbus}. * Protocol:: How communication over @command{bus} works internally. * Rationale:: Why @command{bus}? * GNU Free Documentation License:: Copying and sharing this manual. @@ -348,6 +349,271 @@ running @command{stat} over the file @var{PATHNAME}. +@node Interface +@chapter Interface + +To use @command{libbus} in your C program, include the +header file @file{<bus.h>} and link with the flag +@option{-lbus}. + +With exception to @code{bus_poll} and @code{bus_poll_timed}, +all functions return @code{0} upon successful completion, +and @code{-1} in case of failure. @code{bus_poll} and +@code{bus_poll_timed} return @code{NULL} on failure. +On failure on all functions set @code{errno} to indicate +what went wrong. + +@file{<bus.h>} defines the following functions: + +@table @code +@item int bus_create(const char *file, int flags, char **out_file) +This function creates a bus with the asscoiated pathname +specifed by the value of the parameter @code{file}. If +@code{file} is @code{NULL} a random pathname is selected. +This pathname adheres to the convention set forth by +in @ref{Standard}. + +If @code{file} is not @code{NULL} the function fails if the +file already exists if @code{flags} contains @code{BUS_EXCL}. +Otherwise if @code{file} is not @code{NULL}, the function +does nothing if the file already exists. + +If @code{flags} contains @code{BUS_INTR}, the function fails +if it is interrupted. + +Unless @code{out_file} is NULL, the pathname of the bus +should be stored in a new char array stored in @code{*out_file}. +The caller must free the allocated stored in @code{*out_file}. + +If the processes cannot allocate enough memory to perform +the action, the function sets @code{errno} to @code{ENOMEM} +and fails. It may also fail and set @code{errno} to any of +the errors specified for the system calls @code{open} and +@code{write}. + +@item int bus_unlink(const char *file) +This function removes the bus assoicated with the pathname +stored in the parameter @code{file}. The function also +unlinks the file. + +The function may set @code{errno} to any of the following +values and fail for the specified reasons: +@table @code +@item EINVAL +The bus does not exist. +@item EACCES +Operation permission is denied to the calling process. +@item EPERM +The user does not have permission to remove the bus. +@end table +@noindent +It may also fail and set @code{errno} to any of the errors +specified for the system calls @code{unlink} and @code{open}, +and the functions @code{semget} and @code{shmget}. + +@item int bus_open(bus_t *bus, const char *file, int flags) +This function acquires resources required for the process +to use the bus associated with the filename stored in the +parameter @code{file}. The function also stores the resources +in @code{bus} for use by other @command{bus} functions. + +Values for @code{flags} are constructed by a bitwise +inclusive @sc{or} of flags from the following list. +@table @code +@item BUS_RDONLY +The process will only be using the bus for receiving messages. +@item BUS_WRONLY +The process will only be using the bus for sending messages. +@item BUS_RDWR +The process will use the bus for both receiving and sending +messages. +@end table + +The function may set @code{errno} to any of the following +values and fail for the specified reasons: +@table @code +@item ENOMEM +The process cannot allocate enough memory to perform the +action. +@item EACCES +Operation permission is denied to the calling process. +@item EINVAL +The described bus does not exist. +@end table +@noindent +It may also fail and set @code{errno} to any of the errors +specified for the system call @code{open}. + +@item int bus_close(bus_t *bus) +This function disposes of resources allocated to the +process, as referenced in the parameter @code{bus}. + +The function fails and sets @code{errno} to @code{EINVAL} +if the bus does not exist. + +@item int bus_write(const bus_t *bus, const char *message, int flags) +This function broadcasts a message on the bus whose +information is stored in the parameter @code{bus}. The +message read by the function is stored in the parameter +@code{message}. It may not exceeed 2048 bytes, including +NUL termination. + +The function shall fail, and set @code{errno} to +@code{EAGAIN}, if the call would suspend the process and +@code{flags} contains @code{BUS_NOWAIT}. + +The function may fail and set @code{errno} to any of the +errors specified for the function @code{semop}. + +@item int bus_write_timed(const bus_t *bus, const char *message, const struct timespec *timeout, clockid_t clockid) +This function behaves like @code{bus_write}, except if it +is not able to write the message within the specified time, +it will fail and set @code{errno} to @code{EAGAIN}. The +time is specified as an absolute time using the parameter +@code{timeout}. The behaviour is unspecified if @code{timeout} +is @code{NULL}. @code{timeout} is measured with the clock whose +identifier is specified by the parameter @code{clockid}. This +clock must be a predicitable clock@footnote{There are probably +other, undocumented, seemingly arbitrary restrictions too.}. + +The function may fail and set @code{errno} to any of the +errors specified for the functions @code{semop} and +@code{clock_gettime}. + +@item int bus_read(const bus_t *bus, int (*callback)(const char *message, void *user_data), void *user_data) +This function waits for new message to be sent on the bus +specified in the @code{bus} parameter, as provieded by a +previous call to the function @code{bus_open}. Once a +message is received, the parameter-function @code{callback} +is invoked. The parameter @code{message} in @code{callback} +is the received message, and @code{user_data} in +@code{callback} should be @code{user_data} from @code{bus_read}. +However, once the function [@code{bus_read}] has ensured +that it will receive any message sent on the bus, it shall +invoke the parameter-function @code{callback} with +@code{message} set to @code{NULL}, to notify the process that +it can perform any action that requires that it is listening +on the bus. + +After @code{callback} returns, @code{message} may be override. +Therefore @code{callback} should copy message and start a new +thread that uses the copy of @code{message}. @code{callback} +shall return @code{-1} on failure, @code{0} if the function +[@code{bus_read}] should stop listening, or @code{1} if +the function should continue listening. + +The function may fail and set @code{errno} to any of the +errors specified for the function @code{semop}. + +@item int bus_read_timed(const bus_t *bus, int (*callback)(const char *message, void *user_data), void *user_data, const struct timespec *timeout, clockid_t clockid) +This function behaves like @code{bus_read}, except it will +automatically fail and set @code{errno} to @code{EAGAIN} when +the specified time has passed. The time is specified as an +absolute time using the parameter @code{timeout}. The +behaviour is unspecified if @code{timeout} is @code{NULL}. +@code{timeout} is measured with the clock whose identifier +is specified by the parameter @code{clockid}. This clock +must be a predicitable clock@footnote{There are probably +other, undocumented, seemingly arbitrary restrictions too.}. + +The function may fail and set @code{errno} to any of the +errors specified for the functions @code{semop} and +@code{clock_gettime}. + +@item int bus_poll_start(bus_t *bus) +@itemx int bus_poll_stop(const bus_t *bus) +@itemx const char *bus_poll(bus_t *bus, int flags) +@itemx const char *bus_poll_timed(bus_t *bus, const struct timespec *timeout, clockid_t clockid) +The function @code{bus_poll} waits for a message to be +broadcasted on the bus, and return the message it receives. +The function fails if @code{flags} contains @code{BUS_NOWAIT} +and there is not already a message waiting on the bus. +Received messages shall be copied and parsed, and acted +upon, in a separate thread, and the function @code{bus_poll} +or the function @code{bus_poll_stop} called again as soon +as possible. + +The funcion @code{bus_poll_start} must be called before +@code{bus_poll} is called for the first time. When the +process is done listening on the bus, it must call the +function @code{bus_poll_stop}. + +The function @code{bus_poll_timed} behaves like the function +@code{bus_poll}, except if it is not able to read a message +within the specified time, it will fail and set @code{errno} +to @code{EAGAIN}. The time is specified as an absolute time +using the parameter @code{timeout}. The behaviour is +unspecified if @code{timeout} is @code{NULL}. @code{timeout} +is measured with the clock whose identifier is specified by +the parameter @code{clockid}. This clock must be a predicitable +clock@footnote{There are probably other, undocumented, +seemingly arbitrary restrictions too.}. + +Upon successful completion, the functions @code{bus_poll} and +@code{bus_poll_timed} returns the received message. + +These functions may fail and set @code{errno} to any of the +errors specified for the function @code{semop}. The function +@code{bus_poll_timed} may also set @code{errno} to any of +the errors specified for @code{clock_gettime}. + +@item int bus_chown(const char *file, uid_t owner, gid_t group) +This function changes the owner and the group of the bus, +associated with the file whose pathname is stored in the +parameter @code{file}, to the owner and group specified by +the parameters @code{owner} and @code{group}, respectively. + +The current ownership of a bus can be retrieved by calling +@code{stat} over the pathname of the bus. + +The function may fail and set @code{errno} to any of the +errors specified for the functions @code{bus_open}, +@code{chown}, @code{semget}, @code{shmget}, and @code{shmctl} +as well as any errors specified for the commands +@code{IPC_STAT} and @code{IPC_SET} for the function +@code{semctl}. + +@item int bus_chmod(const char *file, mode_t mode) +This function gives access to the bus associated with the +file whose pathname is stored in the parameter @code{file} +according to the following rules: + +@itemize @bullet{} +@item +If @code{mode} contains any of the bits @code{S_IRWXU} +contains, the owner should be given full access to the +bus. Otherwise the owner should have no access. +@item +If @code{mode} contains any of the bits @code{S_IRWXG} +contains, the group should be given read and write +access to the bus. Otherwise the group should have no +access. +@item +If @code{mode} contains any of the bits @code{S_IRWXO} +contains, users that are neither the owner nor member +of the group should be given read and write access to +the bus. Otherwise they should have no access. +@end itemize + +The current permissions of a bus can be retrieved by calling +@code{stat} over the pathname of the bus. + +The function may fail and set @code{errno} to any of the +errors specified for the functions @code{bus_open}, +@code{chmode}, @code{semget}, @code{shmget}, and @code{shmctl} +as well as any errors specified for the commands +@code{IPC_STAT} and @code{IPC_SET} for the function +@code{semctl}. +@end table + +There is not reason for poking around in @code{bus_t} +(@code{struct bus}). It should be considered opaque. +You can read the documentation in @file{<bus.h>} if +you want to know what is in it. + + + + @node Protocol @chapter Protocol |