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53f2a2eba9
Binary-only compiler and library, plus documentation and include files for compiling new programs.
199 lines
5.0 KiB
Plaintext
Executable File
199 lines
5.0 KiB
Plaintext
Executable File
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READ(2V) SYSTEM CALLS READ(2V)
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NAME
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read, readv - read input
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SYNOPSIS
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cc = read(d, buf, nbytes)
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int cc, d;
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char *buf;
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int nbytes;
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#include <sys/types.h>
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#include <sys/uio.h>
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cc = readv(d, iov, iovcnt)
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int cc, d;
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struct iovec *iov;
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int iovcnt;
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DESCRIPTION
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read attempts to read nbytes of data from the object refer-
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enced by the descriptor d into the buffer pointed to by buf.
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readv performs the same action, but scatters the input data
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into the iovcnt buffers specified by the members of the iov
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array: iov[0], iov[1], ..., iov[iovcnt-1].
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For readv, the iovec structure is defined as
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struct iovec {
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caddr_t iov_base;
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int iov_len;
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};
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Each iovec entry specifies the base address and length of an
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area in memory where data should be placed. readv will
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always fill an area completely before proceeding to the
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next.
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On objects capable of seeking, the read starts at a position
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given by the pointer associated with d (see lseek(2)). Upon
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return from read, the pointer is incremented by the number
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of bytes actually read.
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Objects that are not capable of seeking always read from the
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current position. The value of the pointer associated with
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such an object is undefined.
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Upon successful completion, read and readv return the number
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of bytes actually read and placed in the buffer. The system
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guarantees to read the number of bytes requested if the
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descriptor references a normal file which has that many
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bytes left before the end-of-file, but in no other case.
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Sun Release 3.4 Last change: 25 July 1986 1
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READ(2V) SYSTEM CALLS READ(2V)
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If the returned value is 0, then end-of-file has been
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reached.
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When attempting to read from a descriptor associated with an
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empty pipe, socket, or FIFO:
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If O_NDELAY is set, the read will return a -1 and errno
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will be set to EWOULDBLOCK.
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If O_NDELAY is clear, the read will block until data is
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written to the pipe or the file is no longer open for
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writing.
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When attempting to read from a descriptor associated with a
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tty that has no data currently available:
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If O_NDELAY is set, the read will return a -1 and errno
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will be set to EWOULDBLOCK.
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If O_NDELAY is clear, the read will block until data
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becomes available.
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If O_NDELAY is set, and less data are available than are
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requested by the read or readv, only the data that are
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available are returned, and the count indicates how many
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bytes of data were actually read.
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SYSTEM V DESCRIPTION
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When an attempt is made to read a descriptor which is in
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no-delay mode, and there is no data currently available,
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read will return a 0 instead of returning a -1 and setting
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errno to EWOULDBLOCK. Note that this is indistinguishable
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from end-of-file.
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RETURN VALUE
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If successful, the number of bytes actually read is
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returned. Otherwise, a -1 is returned and the global vari-
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able errno is set to indicate the error.
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ERRORS
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read and readv will fail if one or more of the following are
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true:
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EBADF d is not a valid file descriptor open for
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reading.
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EISDIR d refers to a directory which is on a file
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system mounted using the NFS.
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EFAULT buf points outside the allocated address
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space.
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Sun Release 3.4 Last change: 25 July 1986 2
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READ(2V) SYSTEM CALLS READ(2V)
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EIO An I/O error occurred while reading from or
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writing to the file system.
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EINTR A read from a slow device was interrupted
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before any data arrived by the delivery of a
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signal.
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EINVAL The pointer associated with d was negative.
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EWOULDBLOCK The file was marked for non-blocking I/O, and
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no data were ready to be read. In addition,
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readv may return one of the following errors:
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EINVAL Iovcnt was less than or equal to 0, or
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greater than 16.
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EINVAL One of the iov_len values in the iov array
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was negative.
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EINVAL The sum of the iov_len values in the iov
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array overflowed a 32-bit integer.
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EFAULT Part of iov points outside the process's
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allocated address space.
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SEE ALSO
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dup(2), fcntl(2), open(2), pipe(2), select(2), socket(2),
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socketpair(2)
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Sun Release 3.4 Last change: 25 July 1986 3
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