GNU/Linux man pages
Livre :
Expressions régulières,
Syntaxe et mise en oeuvre :
GNU/Linux |
RedHat 5.2(Apollo) |
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fcntl(2) |
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fcntl − manipulate file descriptor
#include
<unistd.h>
#include <fcntl.h>
int
fcntl(int fd, int cmd);
int fcntl(int fd, int cmd,
long arg);
fcntl performs one of various miscellaneous operations on fd. The operation in question is determined by cmd:
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F_DUPFD |
Makes arg be a copy of fd, closing fd first if necessary. |
The same functionality can be more easily achieved by using dup2(2).
The old and new descriptors may be used interchangeably. They share locks, file position pointers and flags; for example, if the file position is modified by using lseek on one of the descriptors, the position is also changed for the other.
The two descriptors do not share the close-on-exec flag, however. The close-on-exec flag of the copy is off, meaning that it will be closed on exec.
On success, the new descriptor is returned.
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F_GETFD |
Read the close-on-exec flag. If the low-order bit is 0, the file will remain open across exec, otherwise it will be closed. | ||
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F_SETFD |
Set the close-on-exec flag to the value specified by arg (only the least significant bit is used). | ||
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F_GETFL |
Read the descriptor’s flags (all flags (as set by open(2)) are returned). | ||
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F_SETFL |
Set the descriptor’s flags to the value specified by arg. Only O_APPEND and O_NONBLOCK may be set. |
The flags are shared between copies (made with dup etc.) of the same file descriptor.
The flags and their semantics are described in open(2).
F_GETLK, F_SETLK and F_SETLKW
Manage discretionary file locks. The third argument arg is a pointer to a struct flock (that may be overwritten by this call).
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F_GETLK |
Return the flock structure that prevents us from obtaining the lock, or set the l_type field of the lock to F_UNLCK if there is no obstruction. | ||
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F_SETLK |
The lock is set (when l_type is F_RDLCK or F_WRLCK) or cleared (when it is F_UNLCK). If the lock is held by someone else, this call returns -1 and sets errno to EACCES or EAGAIN. | ||
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F_SETLKW |
Like F_SETLK, but instead of returning an error we wait for the lock to be released. If a signal that is to be caught is received while fcntl() is waiting, it is interrupted and returns immediately (with return value −1 and errno set to EINTR). | ||
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F_GETOWN |
Get the process ID or process group currently receiving SIGIO and SIGURG signals for events on file descriptor fd. Process groups are returned as negative values. | ||
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F_SETOWN |
Set the process ID or process group that will receive SIGIO and SIGURG signals for events on file descriptor fd. Process groups are specified using negative values. |
If you set the O_ASYNC status flag on a file descriptor (either by providing this flag with the open call, or by using the F_SETFL command of fcntl), a SIGIO signal is sent whenever input or output becomes possible on that file descriptor. The process or process group to receive the signal can be selected by using the F_SETOWN command to the fcntl function. If the file descriptor is a socket, this also selects the recipient of SIGURG signals that are delivered when out-of-band data arrives on that socket. (SIGURG is sent in any situation where select would report the socket as having an "exceptional condition".) If the file descriptor corresponds to a terminal device, then SIGIO signals are sent to the foreground process group of the terminal.
The use of O_ASYNC, F_GETOWN, F_SETOWN is BSD-specific. POSIX has asynchronous I/O and the aio_sigevent structure to achieve similar things.
For a successful call, the return value depends on the operation:
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F_DUPFD |
The new descriptor. | ||
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F_GETFD |
Value of flag. | ||
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F_GETFL |
Value of flags. | ||
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F_GETOWN |
Value of descriptor owner. | ||
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F_SETFD, |
F_SETFL, F_GETLK, F_SETLK, F_SETLKW Some value different from −1. |
On error, −1 is returned, and errno is set appropriately.
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EACCES |
Operation is prohibited by locks held by other processes. | ||
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EAGAIN |
Operation is prohibited because the file has been memory-mapped by another process. | ||
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EDEADLK |
It was detected that the specified F_SETLKW command would cause a deadlock. | ||
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EBADF |
fd is not an open file descriptor. | ||
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EINTR |
The F_SETLKW command was interrupted by a signal. | ||
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EINVAL |
For F_DUPFD, arg is negative or is greater than the maximum allowable value. | ||
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EMFILE |
For F_DUPFD, the process already has the maximum number of file descriptors open. | ||
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ENOLCK |
Too many segment locks open, lock table is full. |
The errors returned by dup2 are different from those returned by F_DUPFD.
SVr4, SVID, POSIX, X/OPEN, BSD 4.3. Only the operations F_DUPFD, F_GETFD, F_SETFD, F_GETFL, F_SETFL, F_GETLK, F_SETLK and F_SETLKW are specified in POSIX.1; F_GETOWN and F_SETOWN are BSDisms not supported in SVr4. The flags legal for F_GETFL/F_SETFL are those supported by open(2) and vary between these systems; O_APPEND, O_NONBLOCK, O_RDONLY, and O_RDWR are specified in POSIX.1. SVr4 supports several other options and flags not documented here.
POSIX.1 documents an additional EINTR condition. SVr4 documents additional EFAULT, EINTR, EIO, ENOLINK and EOVERFLOW error conditions.
dup2(2), open(2), socket(2), flock(2)
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fcntl(2) | |