accept(3) accept(3) bind(3) bind(3) accept − accept a connection on a socket

accept(3) accept(3) bind(3) bind(3) accept − accept a connection on a socket
accept(3)
accept(3)
bind(3)
bind(3)
NAME
NAME
bind − bind a name to a socket
accept − accept a connection on a socket
SYNOPSIS
SYNOPSIS
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <sys/socket.h>
int bind(int s, const struct sockaddr *name, int namelen);
int accept(int s, struct sockaddr *addr, int *addrlen);
DESCRIPTION
DESCRIPTION
The argument s is a socket that has been created with socket(3N) and bound to an address with bind(3N),
and that is listening for connections after a call to listen(3N). The accept( ) function extracts the first connection on the queue of pending connections, creates a new socket with the properties of s, and allocates a
new file descriptor, ns, for the socket. If no pending connections are present on the queue and the socket is
not marked as non-blocking, accept( ) blocks the caller until a connection is present. If the socket is
marked as non-blocking and no pending connections are present on the queue, accept( ) returns an error as
described below. The accept( ) function uses the netconfig(4) file to determine the STREAMS device file
name associated with s. This is the device on which the connect indication will be accepted. The accepted
socket, ns, is used to read and write data to and from the socket that connected to ns; it is not used to accept
more connections. The original socket (s) remains open for accepting further connections.
bind( ) assigns a name to an unnamed socket. When a socket is created with socket(3N), it exists in a name
space (address family) but has no name assigned. bind( ) requests that the name pointed to by name be
assigned to the socket.
RETURN VALUES
If the bind is successful, 0 is returned. A return value of −1 indicates an error, which is further specified in
the global errno.
ERRORS
The bind( ) call will fail if:
EACCES
The requested address is protected and the current user has inadequate permission
to access it.
The argument addr is a result parameter that is filled in with the address of the connecting entity as it is
known to the communications layer. The exact format of the addr parameter is determined by the domain
in which the communication occurs.
EADDRINUSE
The specified address is already in use.
EADDRNOTAVAIL
The specified address is not available on the local machine.
The argument addrlen is a value-result parameter. Initially, it contains the amount of space pointed to by
addr; on return it contains the length in bytes of the address returned.
EBADF
s is not a valid descriptor.
The accept( ) function is used with connection-based socket types, currently with SOCK_STREAM.
EINVAL
namelen is not the size of a valid address for the specified address family.
It is possible to select(3C) or poll(2) a socket for the purpose of an accept( ) by selecting or polling it for a
read. However, this will only indicate when a connect indication is pending; it is still necessary to call
accept( ).
EINVAL
The socket is already bound to an address.
ENOSR
There were insufficient STREAMS resources for the operation to complete.
ENOTSOCK
s is a descriptor for a file, not a socket.
RETURN VALUES
The following errors are specific to binding names in the UNIX domain:
The accept( ) function returns −1 on error. If it succeeds, it returns a non-negative integer that is a descriptor for the accepted socket.
EACCES
ERRORS
Search permission is denied for a component of the path prefix of the pathname in
name.
accept( ) will fail if:
EIO
An I/O error occurred while making the directory entry or allocating the inode.
EBADF
The descriptor is invalid.
EISDIR
A null pathname was specified.
EINTR
The accept attempt was interrupted by the delivery of a signal.
ELOOP
Too many symbolic links were encountered in translating the pathname in name.
The per-process descriptor table is full.
ENOENT
A component of the path prefix of the pathname in name does not exist.
ENODEV
The protocol family and type corresponding to s could not be found in the netconfig file.
ENOTDIR
A component of the path prefix of the pathname in name is not a directory.
EROFS
The inode would reside on a read-only file system.
ENOMEM
There was insufficient user memory available to complete the operation.
SEE ALSO
EPROTO
A protocol error has occurred; for example, the STREAMS protocol stack has not
been initialized or the connection has already been released.
NOTES
EMFILE
EWOULDBLOCK
The socket is marked as non-blocking and no connections are present to be
accepted.
unlink(2), socket(3N), attributes(5), socket(5)
Binding a name in the UNIX domain creates a socket in the file system that must be deleted by the caller
when it is no longer needed (using unlink(2)).
The rules used in name binding vary between communication domains.
SEE ALSO
poll(2), bind(3N), connect(3N), listen(3N), select(3C), socket(3N), netconfig(4), attributes(5), socket(5)
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opendir/readdir(3)
opendir/readdir(3)
NAME
fopen/fdopen(3)
fopen/fdopen(3)
NAME
opendir − open a directory / readdir − read a directory
fopen, fdopen − stream open functions
SYNOPSIS
SYNOPSIS
#include <sys/types.h>
#include <stdio.h>
#include <dirent.h>
FILE *fopen(const char * path, const char *mode);
FILE *fdopen(int fildes, const char *mode);
DIR *opendir(const char *name);
DESCRIPTION
The fopen function opens the file whose name is the string pointed to by path and associates a stream with
it.
struct dirent *readdir(DIR *dir);
int readdir_r(DIR *dirp, struct dirent *entry, struct dirent **result);
The argument mode points to a string beginning with one of the following sequences (Additional characters
may follow these sequences.):
DESCRIPTION opendir
The opendir() function opens a directory stream corresponding to the directory name, and returns a pointer
to the directory stream. The stream is positioned at the first entry in the directory.
RETURN VALUE
r
Open text file for reading. The stream is positioned at the beginning of the file.
r+
Open for reading and writing. The stream is positioned at the beginning of the file.
w
Truncate file to zero length or create text file for writing. The stream is positioned at the beginning
of the file.
w+
Open for reading and writing. The file is created if it does not exist, otherwise it is truncated. The
stream is positioned at the beginning of the file.
a
Open for appending (writing at end of file). The file is created if it does not exist. The stream is
positioned at the end of the file.
a+
Open for reading and appending (writing at end of file). The file is created if it does not exist.
The stream is positioned at the end of the file.
The opendir() function returns a pointer to the directory stream or NULL if an error occurred.
DESCRIPTION readdir
The readdir() function returns a pointer to a dirent structure representing the next directory entry in the
directory stream pointed to by dir. It returns NULL on reaching the end-of-file or if an error occurred.
DESCRIPTION readdir_r
The readdir_r() function initializes the structure referenced by entry and stores a pointer to this structure
in result. On successful return, the pointer returned at *result will have the same value as the argument
entry. Upon reaching the end of the directory stream, this pointer will have the value NULL.
The data returned by readdir() is overwritten by subsequent calls to readdir() for the same directory
stream.
The dirent structure is defined as follows:
struct dirent {
long
d_ino;
/* inode number */
off_t
d_off;
/* offset to the next dirent */
unsigned short d_reclen;
/* length of this record */
unsigned char d_type;
/* type of file */
char
d_name[256]; /* filename */
};
The fdopen function associates a stream with the existing file descriptor, fildes. The mode of the stream
(one of the values "r", "r+", "w", "w+", "a", "a+") must be compatible with the mode of the file descriptor.
The file position indicator of the new stream is set to that belonging to fildes, and the error and end-of-file
indicators are cleared. Modes "w" or "w+" do not cause truncation of the file. The file descriptor is not
dup’ed, and will be closed when the stream created by fdopen is closed. The result of applying fdopen to a
shared memory object is undefined.
RETURN VALUE
Upon successful completion fopen, fdopen and freopen return a FILE pointer. Otherwise, NULL is
returned and the global variable errno is set to indicate the error.
ERRORS
EINVAL
The mode provided to fopen, fdopen, or freopen was invalid.
RETURN VALUE
The readdir() function returns a pointer to a dirent structure, or NULL if an error occurs or end-of-file is
reached.
readdir_r() returns 0 if successful or an error number to indicate failure.
The fopen, fdopen and freopen functions may also fail and set errno for any of the errors specified for the
routine malloc(3).
The fopen function may also fail and set errno for any of the errors specified for the routine open(2).
The fdopen function may also fail and set errno for any of the errors specified for the routine fcntl(2).
ERRORS
SEE ALSO
EACCES
Permission denied.
open(2), fclose(3), fileno(3)
ENOENT
Directory does not exist, or name is an empty string.
ENOTDIR
name is not a directory.
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ip(7)
ip(7)
NAME
malloc(3)
malloc(3)
NAME
ip − Linux IPv4 protocol implementation
calloc, malloc, free, realloc − Allocate and free dynamic memory
SYNOPSIS
SYNOPSIS
#include <sys/socket.h>
#include <netinet/in.h>
#include <stdlib.h>
void *calloc(size_t nmemb, size_t size);
void *malloc(size_t size);
void free(void *ptr);
void *realloc(void *ptr, size_t size);
tcp_socket = socket(PF_INET, SOCK_STREAM, 0);
raw_socket = socket(PF_INET, SOCK_RAW, protocol);
udp_socket = socket(PF_INET, SOCK_DGRAM, protocol);
DESCRIPTION
DESCRIPTION
The programmer’s interface is BSD sockets compatible. For more information on sockets, see socket(7).
An IP socket is created by calling the socket(2) function as socket(PF_INET, socket_type, protocol).
Valid socket types are SOCK_STREAM to open a tcp(7) socket, SOCK_DGRAM to open a udp(7)
socket, or SOCK_RAW to open a raw(7) socket to access the IP protocol directly. protocol is the IP protocol in the IP header to be received or sent. The only valid values for protocol are 0 and IPPROTO_TCP
for TCP sockets and 0 and IPPROTO_UDP for UDP sockets.
When a process wants to receive new incoming packets or connections, it should bind a socket to a local
interface address using bind(2). Only one IP socket may be bound to any given local (address, port) pair.
When INADDR_ANY is specified in the bind call the socket will be bound to all local interfaces. When
listen(2) or connect(2) are called on a unbound socket the socket is automatically bound to a random free
port with the local address set to INADDR_ANY.
calloc() allocates memory for an array of nmemb elements of size bytes each and returns a pointer to the
allocated memory. The memory is set to zero.
malloc() allocates size bytes and returns a pointer to the allocated memory. The memory is not cleared.
free() frees the memory space pointed to by ptr, which must have been returned by a previous call to malloc(), calloc() or realloc(). Otherwise, or if free( ptr) has already been called before, undefined behaviour
occurs. If ptr is NULL, no operation is performed.
realloc() changes the size of the memory block pointed to by ptr to size bytes. The contents will be
unchanged to the minimum of the old and new sizes; newly allocated memory will be uninitialized. If ptr
is NULL, the call is equivalent to malloc(size); if size is equal to zero, the call is equivalent to free( ptr).
Unless ptr is NULL, it must have been returned by an earlier call to malloc(), calloc() or realloc().
RETURN VALUE
ADDRESS FORMAT
An IP socket address is defined as a combination of an IP interface address and a port number. The basic IP
protocol does not supply port numbers, they are implemented by higher level protocols like tcp(7).
struct sockaddr_in {
sa_family_t
sin_family;
u_int16_t
sin_port;
struct in_addr sin_addr;
};
/* Internet address. */
struct in_addr {
u_int32_t
s_addr;
};
For calloc() and malloc(), the value returned is a pointer to the allocated memory, which is suitably aligned
for any kind of variable, or NULL if the request fails.
free() returns no value.
realloc() returns a pointer to the newly allocated memory, which is suitably aligned for any kind of variable
and may be different from ptr, or NULL if the request fails. If size was equal to 0, either NULL or a
pointer suitable to be passed to free() is returned. If realloc() fails the original block is left untouched - it is
not freed or moved.
/* address family: AF_INET */
/* port in network byte order */
/* internet address */
CONFORMING TO
ANSI-C
SEE ALSO
/* address in network byte order */
brk(2), posix_memalign(3)
sin_family is always set to AF_INET. This is required; in Linux 2.2 most networking functions return
EINVAL when this setting is missing. sin_port contains the port in network byte order. The port numbers
below 1024 are called reserved ports. Only processes with effective user id 0 or the
CAP_NET_BIND_SERVICE capability may bind(2) to these sockets.
sin_addr is the IP host address. The addr member of struct in_addr contains the host interface address in
network order. in_addr should be only accessed using the inet_aton(3), inet_addr(3), inet_makeaddr(3)
library functions or directly with the name resolver (see gethostbyname(3)).
Note that the address and the port are always stored in network order. In particular, this means that you
need to call htons(3) on the number that is assigned to a port. All address/port manipulation functions in
the standard library work in network order.
SEE ALSO
sendmsg(2), recvmsg(2), socket(7), netlink(7), tcp(7), udp(7), raw(7), ipfw(7)
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PTHREAD_COND(3)
PTHREAD_COND(3)
NAME
pthread_cond_init,
pthread_cond_destroy,
pthread_cond_signal,
pthread_cond_wait, pthread_cond_timedwait − operations on conditions
pthread_cond_broadcast,
PTHREAD_COND(3)
PTHREAD_COND(3)
signaled (and thus ignored) between the time a thread locks the mutex and the time it waits on the condition
variable.
pthread_cond_timedwait atomically unlocks mutex and waits on cond, as pthread_cond_wait does, but it
also bounds the duration of the wait. If cond has not been signaled within the amount of time specified by
abstime, the mutex mutex is re-acquired and pthread_cond_timedwait returns the error ETIMEDOUT.
The abstime parameter specifies an absolute time, with the same origin as time(2) and gettimeofday(2): an
abstime of 0 corresponds to 00:00:00 GMT, January 1, 1970.
SYNOPSIS
#include <pthread.h>
pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
pthread_cond_destroy destroys a condition variable, freeing the resources it might hold. No threads must
be waiting on the condition variable on entrance to pthread_cond_destroy. In the LinuxThreads implementation, no resources are associated with condition variables, thus pthread_cond_destroy actually does
nothing except checking that the condition has no waiting threads.
int pthread_cond_init(pthread_cond_t *cond, pthread_condattr_t *cond_attr);
int pthread_cond_signal(pthread_cond_t *cond);
int pthread_cond_broadcast(pthread_cond_t *cond);
CANCELLATION
int pthread_cond_wait(pthread_cond_t *cond, pthread_mutex_t *mutex);
int pthread_cond_timedwait(pthread_cond_t *cond, pthread_mutex_t *mutex, const struct timespec
*abstime);
int pthread_cond_destroy(pthread_cond_t *cond);
ASYNC-SIGNAL SAFETY
DESCRIPTION
A condition (short for ‘‘condition variable’’) is a synchronization device that allows threads to suspend
execution and relinquish the processors until some predicate on shared data is satisfied. The basic operations on conditions are: signal the condition (when the predicate becomes true), and wait for the condition,
suspending the thread execution until another thread signals the condition.
A condition variable must always be associated with a mutex, to avoid the race condition where a thread
prepares to wait on a condition variable and another thread signals the condition just before the first thread
actually waits on it.
pthread_cond_init initializes the condition variable cond, using the condition attributes specified in
cond_attr, or default attributes if cond_attr is NULL. The LinuxThreads implementation supports no
attributes for conditions, hence the cond_attr parameter is actually ignored.
Variables of type pthread_cond_t
PTHREAD_COND_INITIALIZER.
can
also
pthread_cond_wait and pthread_cond_timedwait are cancellation points. If a thread is cancelled while
suspended in one of these functions, the thread immediately resumes execution, then locks again the mutex
argument to pthread_cond_wait and pthread_cond_timedwait, and finally executes the cancellation.
Consequently, cleanup handlers are assured that mutex is locked when they are called.
be
initialized
statically,
using
the
The condition functions are not async-signal safe, and should not be called from a signal handler. In particular, calling pthread_cond_signal or pthread_cond_broadcast from a signal handler may deadlock the
calling thread.
RETURN VALUE
All condition variable functions return 0 on success and a non-zero error code on error.
ERRORS
pthread_cond_init, pthread_cond_signal, pthread_cond_broadcast, and pthread_cond_wait never
return an error code.
The pthread_cond_timedwait function returns the following error codes on error:
ETIMEDOUT
the condition variable was not signaled until the timeout specified by abstime
constant
EINTR
pthread_cond_signal restarts one of the threads that are waiting on the condition variable cond. If no
threads are waiting on cond, nothing happens. If several threads are waiting on cond, exactly one is
restarted, but it is not specified which.
pthread_cond_timedwait was interrupted by a signal
The pthread_cond_destroy function returns the following error code on error:
EBUSY
pthread_cond_broadcast restarts all the threads that are waiting on the condition variable cond. Nothing
happens if no threads are waiting on cond.
pthread_cond_wait atomically unlocks the mutex (as per pthread_unlock_mutex) and waits for the condition variable cond to be signaled. The thread execution is suspended and does not consume any CPU time
until the condition variable is signaled. The mutex must be locked by the calling thread on entrance to
pthread_cond_wait. Before returning to the calling thread, pthread_cond_wait re-acquires mutex (as per
pthread_lock_mutex).
some threads are currently waiting on cond.
AUTHOR
Xavier Leroy <[email protected]>
SEE ALSO
pthread_condattr_init(3),
nanosleep(2).
pthread_mutex_lock(3),
pthread_mutex_unlock(3),
gettimeofday(2),
Unlocking the mutex and suspending on the condition variable is done atomically. Thus, if all threads
always acquire the mutex before signaling the condition, this guarantees that the condition cannot be
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PTHREAD_CREATE(3)
PTHREAD_CREATE(3)
PTHREAD_MUTEX(3)
PTHREAD_MUTEX(3)
NAME
NAME
pthread_mutex_init,
pthread_mutex_lock,
pthread_mutex_destroy − operations on mutexes
pthread_create − create a new thread
pthread_mutex_trylock,
pthread_mutex_unlock,
SYNOPSIS
#include <pthread.h>
SYNOPSIS
#include <pthread.h>
int pthread_create(pthread_t * thread, pthread_attr_t * attr, void * (*start_routine)(void *), void *
arg);
pthread_mutex_t fastmutex = PTHREAD_MUTEX_INITIALIZER;
pthread_mutex_t recmutex = PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP;
DESCRIPTION
pthread_create creates a new thread of control that executes concurrently with the calling thread. The new
thread applies the function start_routine passing it arg as first argument. The new thread terminates either
explicitly, by calling pthread_exit(3), or implicitly, by returning from the start_routine function. The latter
case is equivalent to calling pthread_exit(3) with the result returned by start_routine as exit code.
The attr argument specifies thread attributes to be applied to the new thread. See pthread_attr_init(3) for a
complete list of thread attributes. The attr argument can also be NULL, in which case default attributes are
used: the created thread is joinable (not detached) and has default (non real-time) scheduling policy.
pthread_mutex_t errchkmutex = PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP;
int pthread_mutex_init(pthread_mutex_t *mutex, const pthread_mutexattr_t *mutexattr);
int pthread_mutex_lock(pthread_mutex_t *mutex);
int pthread_mutex_trylock(pthread_mutex_t *mutex);
int pthread_mutex_unlock(pthread_mutex_t *mutex);
RETURN VALUE
On success, the identifier of the newly created thread is stored in the location pointed by the thread argument, and a 0 is returned. On error, a non-zero error code is returned.
int pthread_mutex_destroy(pthread_mutex_t *mutex);
DESCRIPTION
ERRORS
A mutex is a MUTual EXclusion device, and is useful for protecting shared data structures from concurrent
modifications, and implementing critical sections and monitors.
EAGAIN
not enough system resources to create a process for the new thread.
A mutex has two possible states: unlocked (not owned by any thread), and locked (owned by one thread). A
mutex can never be owned by two different threads simultaneously. A thread attempting to lock a mutex
that is already locked by another thread is suspended until the owning thread unlocks the mutex first.
EAGAIN
more than PTHREAD_THREADS_MAX threads are already active.
AUTHOR
pthread_mutex_init initializes the mutex object pointed to by mutex according to the mutex attributes
specified in mutexattr. If mutexattr is NULL, default attributes are used instead.
Xavier Leroy <[email protected]>
The LinuxThreads implementation supports only one mutex attributes, the mutex kind, which is either
‘‘fast’’, ‘‘recursive’’, or ‘‘error checking’’. The kind of a mutex determines whether it can be locked again
by a thread that already owns it. The default kind is ‘‘fast’’. See pthread_mutexattr_init(3) for more
information on mutex attributes.
SEE ALSO
pthread_exit(3), pthread_join(3), pthread_detach(3), pthread_attr_init(3).
Variables of type pthread_mutex_t can also be initialized statically, using the constants
PTHREAD_MUTEX_INITIALIZER (for fast mutexes), PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP (for recursive mutexes), and PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP (for error checking mutexes).
pthread_mutex_lock locks the given mutex. If the mutex is currently unlocked, it becomes locked and
owned by the calling thread, and pthread_mutex_lock returns immediately. If the mutex is already locked
by another thread, pthread_mutex_lock suspends the calling thread until the mutex is unlocked.
If the mutex is already locked by the calling thread, the behavior of pthread_mutex_lock depends on the
kind of the mutex. If the mutex is of the ‘‘fast’’ kind, the calling thread is suspended until the mutex is
unlocked, thus effectively causing the calling thread to deadlock. If the mutex is of the ‘‘error checking’’
kind, pthread_mutex_lock returns immediately with the error code EDEADLK. If the mutex is of the
‘‘recursive’’ kind, pthread_mutex_lock succeeds and returns immediately, recording the number of times
the calling thread has locked the mutex. An equal number of pthread_mutex_unlock operations must be
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PTHREAD_MUTEX(3)
PTHREAD_MUTEX(3)
performed before the mutex returns to the unlocked state.
socket(3)
socket(3)
NAME
socket − create an endpoint for communication
pthread_mutex_trylock behaves identically to pthread_mutex_lock, except that it does not block the
calling thread if the mutex is already locked by another thread (or by the calling thread in the case of a
‘‘fast’’ mutex). Instead, pthread_mutex_trylock returns immediately with the error code EBUSY.
pthread_mutex_unlock unlocks the given mutex. The mutex is assumed to be locked and owned by the
calling thread on entrance to pthread_mutex_unlock. If the mutex is of the ‘‘fast’’ kind,
pthread_mutex_unlock always returns it to the unlocked state. If it is of the ‘‘recursive’’ kind, it decrements the locking count of the mutex (number of pthread_mutex_lock operations performed on it by the
calling thread), and only when this count reaches zero is the mutex actually unlocked.
On ‘‘error checking’’ mutexes, pthread_mutex_unlock actually checks at run-time that the mutex is
locked on entrance, and that it was locked by the same thread that is now calling pthread_mutex_unlock.
If these conditions are not met, an error code is returned and the mutex remains unchanged. ‘‘Fast’’ and
‘‘recursive’’ mutexes perform no such checks, thus allowing a locked mutex to be unlocked by a thread
other than its owner. This is non-portable behavior and must not be relied upon.
pthread_mutex_destroy destroys a mutex object, freeing the resources it might hold. The mutex must be
unlocked on entrance. In the LinuxThreads implementation, no resources are associated with mutex objects,
thus pthread_mutex_destroy actually does nothing except checking that the mutex is unlocked.
SYNOPSIS
cc [ flag . . . ] file . . . −lsocket −lnsl [ library . . . ]
#include <sys/types.h>
#include <sys/socket.h>
int socket(int domain, int type, int protocol);
DESCRIPTION
socket( ) creates an endpoint for communication and returns a descriptor.
The domain parameter specifies a communications domain within which communication will take place;
this selects the protocol family which should be used. The protocol family generally is the same as the
address family for the addresses supplied in later operations on the socket. These families are defined in
the include file <sys/socket.h>. There must be an entry in the netconfig(4) file for at least each protocol
family and type required. If protocol has been specified, but no exact match for the tuplet family, type, protocol is found, then the first entry containing the specified family and type with zero for protocol will be
used. The currently understood formats are:
PF_UNIX
UNIX system internal protocols
PF_INET
ARPA Internet protocols
The socket has the indicated type, which specifies the communication semantics. Currently defined types
are:
RETURN VALUE
pthread_mutex_init always returns 0. The other mutex functions return 0 on success and a non-zero error
code on error.
ERRORS
The pthread_mutex_lock function returns the following error code on error:
A SOCK_STREAM type provides sequenced, reliable, two-way connection-based byte streams. An out-ofband data transmission mechanism may be supported. A SOCK_DGRAM socket supports datagrams (connectionless, unreliable messages of a fixed (typically small) maximum length). A SOCK_SEQPACKET
socket may provide a sequenced, reliable, two-way connection-based data transmission path for datagrams
of fixed maximum length; a consumer may be required to read an entire packet with each read system call.
This facility is protocol specific, and presently not implemented for any protocol family. SOCK_RAW
sockets provide access to internal network interfaces. The types SOCK_RAW, which is available only to
the super-user, and SOCK_RDM, for which no implementation currently exists, are not described here.
EINVAL
the mutex has not been properly initialized.
EDEADLK
the mutex is already locked by the calling thread (‘‘error checking’’ mutexes only).
The pthread_mutex_unlock function returns the following error code on error:
EINVAL
the mutex has not been properly initialized.
protocol specifies a particular protocol to be used with the socket. Normally only a single protocol exists to
support a particular socket type within a given protocol family. However, multiple protocols may exist, in
which case a particular protocol must be specified in this manner. The protocol number to use is particular
to the “communication domain” in which communication is to take place. If a protocol is specified by the
caller, then it will be packaged into a socket level option request and sent to the underlying protocol layers.
EPERM
the calling thread does not own the mutex (‘‘error checking’’ mutexes only).
Sockets of type SOCK_STREAM are full-duplex byte streams, similar to pipes. A stream socket must be in
a connected state before any data may be sent or received on it. A connection to another socket is created
with a connect(3N) call. Once connected, data may be transferred using read(2) and write(2) calls or
some variant of the send(3N) and recv(3N) calls. When a session has been completed, a close(2) may be
performed. Out-of-band data may also be transmitted as described on the send(3N) manual page and
received as described on the recv(3N) manual page.
The pthread_mutex_destroy function returns the following error code on error:
EBUSY
the mutex is currently locked.
AUTHOR
The communications protocols used to implement a SOCK_STREAM insure that data is not lost or duplicated. If a piece of data for which the peer protocol has buffer space cannot be successfully transmitted
within a reasonable length of time, then the connection is considered broken and calls will indicate an error
with −1 returns and with ETIMEDOUT as the specific code in the global variable errno. The protocols
optionally keep sockets “warm” by forcing transmissions roughly every minute in the absence of other
Xavier Leroy <[email protected]>
SEE ALSO
pthread_mutexattr_init(3), pthread_mutexattr_setkind_np(3), pthread_cancel(3).
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SOCK_STREAM
SOCK_DGRAM
SOCK_RAW
SOCK_SEQPACKET
SOCK_RDM
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socket(3)
socket(3)
stat(2)
activity. An error is then indicated if no response can be elicited on an otherwise idle connection for a
extended period (for instance 5 minutes). A SIGPIPE signal is raised if a process sends on a broken stream;
this causes naive processes, which do not handle the signal, to exit.
NAME
SOCK_SEQPACKET sockets employ the same system calls as SOCK_STREAM sockets. The only difference is that read(2) calls will return only the amount of data requested, and any remaining in the arriving
packet will be discarded.
SOCK_DGRAM and SOCK_RAW sockets allow datagrams to be sent to correspondents named in
sendto(3N) calls. Datagrams are generally received with recvfrom(3N), which returns the next datagram
with its return address.
An fcntl(2) call can be used to specify a process group to receive a SIGURG signal when the out-of-band
data arrives. It may also enable non-blocking I/O and asynchronous notification of I/O events with SIGIO
signals.
The operation of sockets is controlled by socket level options. These options are defined in the file
<sys/socket.h>. setsockopt(3N) and getsockopt(3N) are used to set and get options, respectively.
RETURN VALUES
stat(2)
stat, fstat, lstat − get file status
SYNOPSIS
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
int stat(const char * file_name, struct stat *buf );
int fstat(int filedes, struct stat *buf );
int lstat(const char * file_name, struct stat *buf );
DESCRIPTION
These functions return information about the specified file. You do not need any access rights to the file to
get this information but you need search rights to all directories named in the path leading to the file.
stat stats the file pointed to by file_name and fills in buf .
lstat is identical to stat, except in the case of a symbolic link, where the link itself is stat-ed, not the file that
it refers to.
A −1 is returned if an error occurs. Otherwise the return value is a descriptor referencing the socket.
ERRORS
The socket( ) call fails if:
EACCES
Permission to create a socket of the specified type and/or protocol is denied.
EMFILE
The per-process descriptor table is full.
ENOMEM
Insufficient user memory is available.
ENOSR
There were insufficient STREAMS resources available to complete the operation.
EPROTONOSUPPORT
The protocol type or the specified protocol is not supported within this
domain.
fstat is identical to stat, only the open file pointed to by filedes (as returned by open(2)) is stat-ed in place
of file_name.
They all return a stat structure, which contains the following fields:
SEE ALSO
close(2), fcntl(2), ioctl(2), read(2), write(2), accept(3N), bind(3N), connect(3N), getsockname(3N), getsockopt(3N), listen(3N), recv(3N), setsockopt(3N), send(3N), shutdown(3N), socketpair(3N),
attributes(5), in(5), socket(5)
struct stat {
dev_t
ino_t
mode_t
nlink_t
uid_t
gid_t
dev_t
off_t
blksize_t
blkcnt_t
time_t
time_t
time_t
};
st_dev;
/* device */
st_ino; /* inode */
st_mode; /* protection */
st_nlink; /* number of hard links */
st_uid; /* user ID of owner */
st_gid; /* group ID of owner */
st_rdev; /* device type (if inode device) */
st_size; /* total size, in bytes */
st_blksize; /* blocksize for filesystem I/O */
st_blocks; /* number of blocks allocated */
st_atime; /* time of last access */
st_mtime; /* time of last modification */
st_ctime; /* time of last status change */
The value st_size gives the size of the file (if it is a regular file or a symlink) in bytes. The size of a symlink
is the length of the pathname it contains, without trailing NUL.
The value st_blocks gives the size of the file in 512-byte blocks. (This may be smaller than st_size/512 e.g.
when the file has holes.) The value st_blksize gives the "preferred" blocksize for efficient file system I/O.
(Writing to a file in smaller chunks may cause an inefficient read-modify-rewrite.)
Not all of the Linux filesystems implement all of the time fields. Some file system types allow mounting in
such a way that file accesses do not cause an update of the st_atime field. (See ‘noatime’ in mount(8).)
The field st_atime is changed by file accesses, e.g. by execve(2), mknod(2), pipe(2), utime(2) and read(2)
(of more than zero bytes). Other routines, like mmap(2), may or may not update st_atime.
The field st_mtime is changed by file modifications, e.g. by mknod(2), truncate(2), utime(2) and write(2)
(of more than zero bytes). Moreover, st_mtime of a directory is changed by the creation or deletion of files
in that directory. The st_mtime field is not changed for changes in owner, group, hard link count, or mode.
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stat(2)
stat(2)
strerror(3)
The field st_ctime is changed by writing or by setting inode information (i.e., owner, group, link count,
mode, etc.).
NAME
The following POSIX macros are defined to check the file type:
SYNOPSIS
strerror(3)
strerror, strerror_r − return string describing error code
S_ISREG(m)
is it a regular file?
#include <string.h>
S_ISDIR(m)
directory?
S_ISCHR(m)
character device?
char *strerror(int errnum);
int strerror_r(int errnum, char *buf , size_t n);
S_ISBLK(m)
block device?
S_ISFIFO(m)
fifo?
S_ISLNK(m)
symbolic link? (Not in POSIX.1-1996.)
S_ISSOCK(m)
socket? (Not in POSIX.1-1996.)
DESCRIPTION
The strerror() function returns a string describing the error code passed in the argument errnum, possibly
using the LC_MESSAGES part of the current locale to select the appropriate language. This string must
not be modified by the application, but may be modified by a subsequent call to perror() or strerror(). No
library function will modify this string.
The following flags are defined for the st_mode field:
S_IFMT
S_IFSOCK
S_IFLNK
S_IFREG
S_IFBLK
S_IFDIR
S_IFCHR
S_IFIFO
S_ISUID
S_ISGID
S_ISVTX
S_IRWXU
S_IRUSR
S_IWUSR
S_IXUSR
S_IRWXG
S_IRGRP
S_IWGRP
S_IXGRP
S_IRWXO
S_IROTH
S_IWOTH
S_IXOTH
0170000
0140000
0120000
0100000
0060000
0040000
0020000
0010000
0004000
0002000
0001000
00700
00400
00200
00100
00070
00040
00020
00010
00007
00004
00002
00001
The strerror_r() function is similar to strerror(), but is thread safe. It returns the string in the user-supplied buffer buf of length n.
bitmask for the file type bitfields
socket
symbolic link
regular file
block device
directory
character device
fifo
set UID bit
set GID bit (see below)
sticky bit (see below)
mask for file owner permissions
owner has read permission
owner has write permission
owner has execute permission
mask for group permissions
group has read permission
group has write permission
group has execute permission
mask for permissions for others (not in group)
others have read permission
others have write permisson
others have execute permission
RETURN VALUE
The strerror() function returns the appropriate error description string, or an unknown error message if the
error code is unknown. The value of errno is not changed for a successful call, and is set to a nonzero value
upon error. The strerror_r() function returns 0 on success and −1 on failure, setting errno.
ERRORS
EINVAL
The value of errnum is not a valid error number.
ERANGE
Insufficient storage was supplied to contain the error description string.
CONFORMING TO
SVID 3, POSIX, BSD 4.3, ISO/IEC 9899:1990 (C89).
strerror_r() with prototype as given above is specified by SUSv3, and was in use under Digital Unix and
HP Unix. An incompatible function, with prototype
char *strerror_r(int errnum, char *buf , size_t n);
The set GID bit (S_ISGID) has several special uses: For a directory it indicates that BSD semantics is to be
used for that directory: files created there inherit their group ID from the directory, not from the effective
group ID of the creating process, and directories created there will also get the S_ISGID bit set. For a file
that does not have the group execution bit (S_IXGRP) set, it indicates mandatory file/record locking.
is a GNU extension used by glibc (since 2.0), and must be regarded as obsolete in view of SUSv3. The
GNU version may, but need not, use the user-supplied buffer. If it does, the result may be truncated in case
the supplied buffer is too small. The result is always NUL-terminated.
SEE ALSO
errno(3), perror(3), strsignal(3)
The ‘sticky’ bit (S_ISVTX) on a directory means that a file in that directory can be renamed or deleted only
by the owner of the file, by the owner of the directory, and by a privileged process.
RETURN VALUE
On success, zero is returned. On error, −1 is returned, and errno is set appropriately.
SEE ALSO
chmod(2), chown(2), readlink(2), utime(2), capabilities(7)
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