马可波罗陶瓷江西产地:fcntl中文手册页，翻译的不好，请指正…翻译

来源：百度文库编辑：九乡新闻网时间：2024/07/14 10:58:57

用了一个下午翻译的，有问题请指正
Any problem please contact to chenshengsterATgmail.com http://blog.muduo.net
2004-10-13 17:55

文件控制函数
   fcntl -- file control

LIBRARY
   Standard C Library (libc, -lc)

SYNOPSIS
   #include ;

   int
   fcntl(int fd, int cmd, ...);

DESCRIPTION
   Fcntl() provides for control over descriptors.  The argument fd is a
   descriptor to be operated on by cmd as described below.  Depending on the
   value of cmd, fcntl can take an additional third argument int arg.
[描述]
Fcntl()针对(文件)描述符提供控制.参数fd 是被参数cmd操作(如下面的描述)的的描述符.
针对cmd的值,fcntl能够接受第三个参数int arg

   F_DUPFD Return a new descriptor as follows:
                  o Lowest numbered available descriptor greater than or
                     equal to arg.
                  o Same object references as the original descriptor.
                  o New descriptor shares the same file offset if the
                     object was a file.
                  o Same access mode (read, write or read/write).
                  o Same file status flags (i.e., both file descriptors
                     share the same file status flags).
                  o The close-on-exec flag associated with the new file
                     descriptor is set to remain open across execve(2) sys-
                     tem calls.
F_DUPFD 返回一个如下描述的(文件)描述符:
o 最小的大于或等于arg的一个可用的描述符
o 与原始操作符一样的某对象的引用
o 如果对象是文件(file)的话,返回一个新的描述符,这个描述符与arg 共享相同的偏移量(offset)
o 相同的访问模式(读,写或读/写)
o 相同的文件状态标志(如:两个文件描述符共享相同的状态标志)
o 与新的文件描述符结合在一起的close-on-exec 标志被设置成交叉式访问execve(2)的系统调用

   F_GETFD Get the close-on-exec flag associated with the file descriptor
            fd as FD_CLOEXEC.  If the returned value ANDed with FD_CLOEXEC
            is 0, the file will remain open across exec(), otherwise the
            file will be closed upon execution of exec() (arg is ignored).
F_GETFD 取得与文件描述符fd联合close-on-exec标志,类似FD_CLOEXEC.如果返回值和FD_CLOEXEC进行与运算结果是0的话,文件保持交叉式访问exec(),否则如果通过exec运行的话,文件将被关闭(arg 被忽略)

   F_SETFD Set the close-on-exec flag associated with fd to arg, where
            arg is either 0 or FD_CLOEXEC, as described above.
F_SETFD 如同上面描述的那样,在arg是o或者FD_CLOEXEC将fd的close-on-exec标志设置给arg

   F_GETFL Get descriptor status flags, as described below (arg is
            ignored).
F_GETFL 取得fd的文件状态标志,如同下面的描述一样(arg被忽略)

   F_SETFL Set descriptor status flags to arg.
F_SETFL 设置给arg描述符状态标志

   F_GETOWN Get the process ID or process group currently receiving SIGIO
            and SIGURG signals; process groups are returned as negative
            values (arg is ignored).
F_GETOWN    取得当前正在接收SIGIO或者SIGURG信号的进程id或进程组id,进程组id返回成负值(arg被忽略)

   F_SETOWN Set the process or process group to receive SIGIO and SIGURG
            signals; process groups are specified by supplying arg as neg-
            ative, otherwise arg is interpreted as a process ID.
F_SETOWN 设置将接收SIGIO和SIGURG信号的进程id或进程组id,进程组id通过提供负值的arg来说明,否则,arg将被认为是进程id

   The flags for the F_GETFL and F_SETFL flags are as follows:
   O_NONBLOCK Non-blocking I/O; if no data is available to a read(2) call,
               or if a write(2) operation would block, the read or write
               call returns -1 with the error EAGAIN.

   O_APPEND    Force each write to append at the end of file; corresponds
               to the O_APPEND flag of open(2).

   O_DIRECT    Minimize or eliminate the cache effects of reading and writ-
               ing.  The system will attempt to avoid caching the data you
               read or write.  If it cannot avoid caching the data, it will
               minimize the impact the data has on the cache.  Use of this
               flag can drastically reduce performance if not used with
               care.

   O_ASYNC    Enable the SIGIO signal to be sent to the process group when
               I/O is possible, e.g., upon availability of data to be read.
命令字(cmd)F_GETFL和F_SETFL的标志如下面的描述:
O_NONBLOCK 非阻塞I/O;如果read(2)调用没有可读取的数据,或者如果write(2)操作将阻塞,read或write调用返回-1和EAGAIN错误
O_APPEND 强制每次写(write)操作都添加在文件大的末尾,相当于open(2)的O_APPEND标志
O_DIRECT 最小化或去掉reading和writing的缓存影响.系统将企图避免缓存你的读或写的数据.如果不能够避免缓存,那么它将最小化已经被缓存了的数据造成的影响.如果这个标志用的不够好,将大大的降低性能
O_ASYNC 当I/O可用的时候,允许SIGIO信号发送到进程组,例如:当有数据可以读的时候

   Several commands are available for doing advisory file locking; they all
   operate on the following structure:
   struct flock {
         off_t l_start;       /* starting offset */
         off_t l_len;       /* len = 0 means until end of file */
         pid_t l_pid;       /* lock owner */
         short l_type;       /* lock type: read/write, etc. */
         short l_whence;    /* type of l_start */
   };
   The commands available for advisory record locking are as follows:

advisory档案锁可用的命令有下面这些:
   F_GETLK Get the first lock that blocks the lock description pointed to
            by the third argument, arg, taken as a pointer to a struct
            flock (see above).  The information retrieved overwrites the
            information passed to fcntl() in the flock structure.  If no
            lock is found that would prevent this lock from being created,
            the structure is left unchanged by this function call except
            for the lock type which is set to F_UNLCK.
F_GETLK 通过第三个参数arg(一个指向flock的结构体)取得第一个阻塞lock description指向的的锁.取得的信息将覆盖传到fcntl()的flock结构的信息.如果没有发现能够阻止本次锁(flock)生成的锁,这个结构将不被改变,除非锁的类型被设置成F_UNLCK.

   F_SETLK Set or clear a file segment lock according to the lock
            description pointed to by the third argument, arg, taken as a
            pointer to a struct flock (see above).  F_SETLK is used to
            establish shared (or read) locks (F_RDLCK) or exclusive (or
            write) locks, (F_WRLCK), as well as remove either type of lock
            (F_UNLCK).  If a shared or exclusive lock cannot be set,
            fcntl() returns immediately with EAGAIN.
F_SETLK 按照指向结构体flock的指针的第三个参数arg所描述的锁的信息设置或者清除一个文件segment锁.F_SETLK被用来实现共享(或读)锁(F_RDLCK)或独占(写)锁(F_WRLCK),同样可以去掉这两种锁(F_UNLCK).如果共享锁或独占锁不能被设置,fcntl()将立即返回EAGAIN.

   F_SETLKW This command is the same as F_SETLK except that if a shared or
            exclusive lock is blocked by other locks, the process waits
            until the request can be satisfied.  If a signal that is to be
            caught is received while fcntl() is waiting for a region, the
            fcntl() will be interrupted if the signal handler has not
            specified the SA_RESTART (see sigaction(2)).
F_SETLKW 除了共享锁或独占锁被其他的锁阻塞这种情况外,这个命令和F_SETLK是一样的.如果共享锁或独占锁被其他的锁阻塞,进程将等待直到这个请求能够完成.当fcntl()正在等待文件的某个区域的时候捕捉到一个一个信号,如果这个信号没有被指定SA_RESTART,fcntl将被中断.

   When a shared lock has been set on a segment of a file, other processes
   can set shared locks on that segment or a portion of it.  A shared lock
   prevents any other process from setting an exclusive lock on any portion
   of the protected area.  A request for a shared lock fails if the file
   descriptor was not opened with read access.
当一个共享锁被set到一个文件的某段的时候,其他的进程可以set 共享锁到这个段或这个段的一部分.共享所阻止任何其他进程set独占锁到这段保护区域的任何部分.如果文件描述符没有以读的访问方式打开的话,共享锁的设置请求会失败

   An exclusive lock prevents any other process from setting a shared lock
   or an exclusive lock on any portion of the protected area.  A request for
   an exclusive lock fails if the file was not opened with write access.
独占锁阻止任何其他的进程在这段保护区域任何位置设置共享锁或独占锁.如果文件描述符不是以写的访问方式打开的话,独占锁的请求会失败

   The value of l_whence is SEEK_SET, SEEK_CUR, or SEEK_END to indicate that
   the relative offset, l_start bytes, will be measured from the start of
   the file, current position, or end of the file, respectively.  The value
   of l_len is the number of consecutive bytes to be locked.  If l_len is
   negative, the result is undefined.  The l_pid field is only used with
   F_GETLK to return the process ID of the process holding a blocking lock.
   After a successful F_GETLK request, the value of l_whence is SEEK_SET.
1_whence 的可能值包括SEEK_SET,SEEK_CUR,和SEEK_END,这些值用来说明相对的偏移量,1_start 比特,将分别从文件的开头、当前位置、文档末尾算起,l_len的值是将被连续锁定的比特值.如果l_len是负值,结果将不被定义的.l_pid只跟F_GETLK一起用用来返回拥有这个blocking锁的进程id.一个成功的F_GETLK请求后,l_whence的值将变成SEEK_SET

   Locks may start and extend beyond the current end of a file, but may not
   start or extend before the beginning of the file.  A lock is set to
   extend to the largest possible value of the file offset for that file if
   l_len is set to zero.  If l_whence and l_start point to the beginning of
   the file, and l_len is zero, the entire file is locked.  If an applica-
   tion wishes only to do entire file locking, the flock(2) system call is
   much more efficient. 一个锁能开始于甚至延伸打当前文件的末尾,但是不能开始于或扩展到文件的开头以前.当l_len为0的时候,锁被设置成文件的最大的可能的偏移量.如果l_whence和l_start指向文件的开始位置,并且l_len为0,整个文件将被锁定.如果一个程序只想锁定整个文档,系统调用flock(2)将更有效率

   There is at most one type of lock set for each byte in the file.  Before
   a successful return from an F_SETLK or an F_SETLKW request when the call-
   ing process has previously existing locks on bytes in the region speci-
   fied by the request, the previous lock type for each byte in the speci-
   fied region is replaced by the new lock type.  As specified above under
   the descriptions of shared locks and exclusive locks, an F_SETLK or an
   F_SETLKW request fails or blocks respectively when another process has
   existing locks on bytes in the specified region and the type of any of
   those locks conflicts with the type specified in the request.    文件的每个字节最多只能设置一种类型的锁.在F_SETLK和F_SETLKW成功返回前,如果当前进程拥有一个已经存在的锁,并且锁住的区域在新锁请求的区域内,则先前被设置的锁的每一个字节都将被新设置成新锁的类型.如上面描述共享锁和独占锁说明的那样,当另一个进程在指定的区域拥有任何跟请求的锁类型相冲突的时候,对F_SETLK或F_SETLKW的请求将会失败或被阻塞.

   This interface follows the completely stupid semantics of System V and
   IEEE Std 1003.1-1988 (``POSIX.1'') that require that all locks associated
   with a file for a given process are removed when any file descriptor for
   that file is closed by that process.  This semantic means that applica-
   tions must be aware of any files that a subroutine library may access.
   For example if an application for updating the password file locks the
   password file database while making the update, and then calls
   getpwnam(3) to retrieve a record, the lock will be lost because
   getpwnam(3) opens, reads, and closes the password database.  The database
   close will release all locks that the process has associated with the
   database, even if the library routine never requested a lock on the data-
   base.  Another minor semantic problem with this interface is that locks
   are not inherited by a child process created using the fork(2) function.
   The flock(2) interface has much more rational last close semantics and
   allows locks to be inherited by child processes.  Flock(2) is recommended
   for applications that want to ensure the integrity of their locks when
   using library routines or wish to pass locks to their children.  Note
   that flock(2) and fcntl(2) locks may be safely used concurrently but
   fcntl(F_GETLK) returns -1 in l_pid if the process holding a blocking lock
   previously locked the file descriptor by flock(2).
   这个接口服从System V和IEEE Std 1003.1-1988 (``POSIX.1'')的"当一个进程关闭任何一个文件操作符的时候,这个文件的与给该进程所有关联的锁都会失效"这一相当stupid的语义.这一语义意味着一个子程序库必须很清楚的知道它可能访问某个文件.例如:一个更新password文件的程序在进行更新操作的时候锁住了password文件,然后调用getpwnam(3)来重新取得一条记录,这时候,这个锁就失效了.因为,getpwnam(3)打开,读取,并且关闭了password数据库文件.数据库文件的关闭释放了所有的这个进程拥有的跟这个数据库文件相关的锁,即使这个操作(指getpwnam(3))并不需要跟这个数据库文件相关联的锁.这个接口语义的另一个问题是锁不能被通过fork(2)创建的子进程继承.fork(2)接口有更多合理的理由和允许锁被子进程继承.Flock(2)被推荐用来一个程序希望确保它的锁的完整性以及希望将它的锁传给它的子进程.
   注意:flock(2)和fcntl(2)锁操作能够安全的同时使用但是如果文件描述符已经被另一个进程用flock(2)锁住,fcntl(F_GETLK)的l_pid返回值为-1

   All locks associated with a file for a given process are removed when the
   process terminates.
   当进程结束的时候,某一文件的给定进程的所有相关锁都会被删掉(失效)

   All locks obtained before a call to execve(2) remain in effect until the
   new program releases them.  If the new program does not know about the
   locks, they will not be released until the program exits.
   所有已经拥有的锁在调用execve(2)后依然起作用直到新的程序释放他们.如果新程序不知道这些锁,那么他们一直到程序结束的时候才会被释放.

   A potential for deadlock occurs if a process controlling a locked region
   is put to sleep by attempting to lock the locked region of another
   process.  This implementation detects that sleeping until a locked region
   is unlocked would cause a deadlock and fails with an EDEADLK error.
   潜在的死锁在一个进程控制一个锁住的文件区域,但是在它试图睡眠等待被其他进程控制的锁解锁的时候就会发生.

RETURN VALUES
   Upon successful completion, the value returned depends on cmd as follows:

         F_DUPFD A new file descriptor.

         F_GETFD Value of flag (only the low-order bit is defined).

         F_GETFL Value of flags.

         F_GETOWN Value of file descriptor owner.

         other    Value other than -1.

   Otherwise, a value of -1 is returned and errno is set to indicate the
   error.

返回值
在成功执行的基础上,返回值根据cmd的不同返回
F_DUPFD 一个新的文件描述符
F_GETFD 标志值(只定义了low-order字节)
F_GETFL 标志值
F_GETOWN    文件描述符的所有者的值(我也不是很清楚是什么????)
其他情况,返回-1并且errno被置值来判断错误

ERRORS
   Fcntl() will fail if:
错误
下面的情况Fcntl()会失败

   [EAGAIN]          The argument cmd is F_SETLK, the type of lock (l_type)
                     is a shared lock (F_RDLCK) or exclusive lock
                     (F_WRLCK), and the segment of a file to be locked is already exclusive-locked by another process; or the
                     type is an exclusive lock and some portion of the seg-
                     ment of a file to be locked is already shared-locked
                     or exclusive-locked by another process.
   [EAGAIN] 参数cmd是F_SETLK,锁的类型(l_type)是共享锁(F_RDLCK)或者是独占锁(F_WRLCK),将被锁定的那一段已经被另一个进程用独占锁锁住;锁的类型是独占锁,将被锁定的那一段中有一部分已经被另一个进程用共享锁或独占锁锁住.

   [EBADF]          Fd is not a valid open file descriptor.

                     The argument cmd is F_SETLK or F_SETLKW, the type of
                     lock (l_type) is a shared lock (F_RDLCK), and fd is
                     not a valid file descriptor open for reading.

                     The argument cmd is F_SETLK or F_SETLKW, the type of
                     lock (l_type) is an exclusive lock (F_WRLCK), and fd
                     is not a valid file descriptor open for writing.
[EBADF] Fd不是一个有效的打开的文件描述符.
参数cmd是F_SETLK或F_SETLKW,锁的类型(l_type)是共享锁(F_RDLCK),并且fd不是一个有效的已经打开的可写文件描述符

   [EDEADLK]       The argument cmd is F_SETLKW, and a deadlock condition
                     was detected.
[EDEADLK] 参数cmd是F_SETLKW,检测到一个死锁

   [EINTR]          The argument cmd is F_SETLKW, and the function was
                     interrupted by a signal.
[EINTR] 参数cmd是F_SETLKW,但是这个函数被一个信号中断

   [EINVAL]          Cmd is F_DUPFD and arg is negative or greater than the
                     maximum allowable number (see getdtablesize(2)).

                     The argument cmd is F_GETLK, F_SETLK, or F_SETLKW and
                     the data to which arg points is not valid, or fd
                     refers to a file that does not support locking.
[EINVAL] cmd是F_DEPFD,arg是负值或者比允许的最大值大(参见getdtablesize(2))

参数cmd是F_GETLK,F_SETLK或者F_SETLKW并且指向arg的数据不是有效的,或者fd指向的文件不支持锁

   [EMFILE]          The argument cmd is F_DUPFD and the maximum number of
                     file descriptors permitted for the process are already
                     in use, or no file descriptors greater than or equal
                     to arg are available.
[EMFILE] 参数cmd是F_DUPFD并且进程能用的文件描述符的最大值已经存在,或者不存在比arg大或相等的文件描述符

   [ENOLCK]          The argument cmd is F_SETLK or F_SETLKW, and satisfy-
                     ing the lock or unlock request would result in the
                     number of locked regions in the system exceeding a
                     system-imposed limit.
[ENOLCK] 参数cmd是F_SETLK或F_SETLKW,并且????

   [EPERM]          Cmd is F_SETOWN and the process ID or process group
                     given as an argument is in a different session than
                     the caller.
[EPERM] 参数cmd是F_SETOWN并且作为参数给定的进程ID或者进程组跟调用者不在同一会话中

   [ESRCH]          Cmd is F_SETOWN and the process ID given as argument
                     is not in use.
[ESRCH] 参数cmd是F_SETOWN但是作为参数给定的进程ID并不存在

   In addition, if fd refers to a descriptor open on a terminal device (as
   opposed to a descriptor open on a socket), a cmd of F_SETOWN can fail for
   the same reasons as in tcsetpgrp(3), and a cmd of F_GETOWN for the rea-
   sons as stated in tcgetpgrp(3).
   另外,如果fd引用的文件描述符是一个终端设备(与打开一个socket的描述符相对),cmd是F_SETWON会失败,原因同tcsetpgrp(3),cmd是F_GETOWN会失败,原因同 tcgetpgrp(3)

SEE ALSO
   close(2), execve(2), flock(2), getdtablesize(2), open(2), sigvec(2),
   tcgetpgrp(3), tcsetpgrp(3)

HISTORY
   The fcntl() function call appeared in 4.2BSD.

FreeBSD 4.9                   January 12, 1994                   FreeBSD 4.9

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