READ(2)                              BSD                               READ(2)



NAME
     read, readv - read input

SYNOPSIS
     cc = read(d, buf, nbytes)
     int cc, d;
     char *buf;
     int nbytes;

     #include <sys/types.h>
     #include <sys/uio.h>

     cc = readv(d, iov, iovcnt)
     int cc, d;
     struct iovec *iov;
     int iovcnt;

DESCRIPTION
     read attempts to read nbytes of data from the object referenced by the
     descriptor d into the buffer pointed to by buf.  readv performs the same
     action, but scatters the input data into the iovcnt buffers specified by
     the members of the iov array: iov[0], iov[1], ..., iov[iovcnt-1].

     For readv, the iovec structure is defined as

          struct iovec {
               caddr_t   iov_base;
               int  iov_len;
          };

     Each iovec entry specifies the base address and length of an area in
     memory where data should be placed. readv will always fill an area
     completely before proceeding to the next.

     On objects capable of seeking, the read starts at a position given by the
     pointer associated with d (see lseek(2)).  Upon return from read, the
     pointer is incremented by the number of bytes actually read.

     Objects that are not capable of seeking always read from the current
     position.  The value of the pointer associated with such an object is
     undefined.

     Upon successful completion, read and readv return the number of bytes
     actually read and placed in the buffer.  The system guarantees to read
     the number of bytes requested if the descriptor references a normal file
     that has that many bytes left before the end-of-file, but in no other
     case.

     If the returned value is 0, then end-of-file has been reached.

     Upon successful completion, read marks for update the st_atime field of
     the file.

NOTES
     In prior releases, opening a sparse file (a file containing "holes" in it
     that are not backed up by disk blocks) and reading through it from
     beginning to end would cause disk blocks to be allocated for the sparse
     regions of the file (that is, the file would cease to be sparse).

     At SR10.4, if the file is accessed through ordinary open(2) and read
     calls, is open for read, resides on an SR10.4 node and is NOT currently

     being written by anyone, the sparseness of the file will be "mostly"
     preserved.  (For example, although file data blocks will not be
     allocated, indirect filemap blocks will be.)

ERRORS
     read and readv will fail if one or more of the following are true:

     [EBADF]         d is not a valid file or socket descriptor open for
                     reading.

     [EIO]           An I/O error occurred while reading from the file system.

     [EINTR]         A read from a slow device was interrupted before any data
                     arrived by the delivery of a signal.

     [EINVAL]        The pointer associated with d was negative.

     [EWOULDBLOCK]   The file was marked for non-blocking I/O, and no data
                     were ready to be read.

     In addition, readv may return one of the following errors:

     [EINVAL]        iovcnt was less than or equal to 0, or greater than 16.

     [EINVAL]        One of the iov_len values in the iov array was negative.

     [EINVAL]        The sum of the iov_len values in the iov array overflowed
                     a 32-bit integer.

SEE ALSO
     dup(2), fcntl(2), open(2), pipe(2), select(2), socket(2), socketpair(2)

DIAGNOSTICS
     If successful, the number of bytes actually read is returned.  Otherwise,
     a -1 is returned and the global variable errno is set to indicate the
     error.