OPEN(2)                                                   OPEN(2)

     NAME
          open, create, close - open a file for reading or writing,
          create file

     SYNOPSIS
          #include <u.h>
          #include <libc.h>

          int open(char *file, int omode)

          int create(char *file, int omode, ulong perm)

          int close(int fd)

     DESCRIPTION
          Open opens the file for I/O and returns an associated file
          descriptor.  Omode is one of OREAD, OWRITE, ORDWR, or OEXEC,
          asking for permission to read, write, read and write, or
          execute, respectively.  In addition, there are three values
          that can be ORed with the omode: OTRUNC says to truncate the
          file to zero length before opening it; OCEXEC says to close
          the file when an exec(2) or execl system call is made; and
          ORCLOSE says to remove the file when it is closed (by every-
          one who has a copy of the file descriptor).  Open fails if
          the file does not exist or the user does not have permission
          to open it for the requested purpose (see stat(2) for a
          description of permissions).  The user must have write per-
          mission on the file if the OTRUNC bit is set.  For the open
          system call (unlike the implicit open in exec(2)), OEXEC is
          actually identical to OREAD.

          Create creates a new file or prepares to rewrite an existing
          file, opens it according to omode (as described for open),
          and returns an associated file descriptor.  If the file is
          new, the owner is set to the userid of the creating process
          group; the group to that of the containing directory; the
          permissions to perm ANDed with the permissions of the con-
          taining directory.  If the file already exists, it is trun-
          cated to 0 length, and the permissions, owner, and group
          remain unchanged.  The created file is a directory if the
          DMDIR bit is set in perm, an exclusive-use file if the
          DMEXCL bit is set, and an append-only file if the DMAPPEND
          bit is set.  Exclusive-use files may be open for I/O by only
          one client at a time, but the file descriptor may become
          invalid if no I/O is done for an extended period; see
          open(5).

          Create fails if the path up to the last element of file can-
          not be evaluated, if the user doesn't have write permission
          in the final directory, if the file already exists and does

     OPEN(2)                                                   OPEN(2)

          not permit the access defined by omode, or if there are no
          free file descriptors.  In the last case, the file may be
          created even when an error is returned.  If the file is new
          and the directory in which it is created is a union direc-
          tory (see intro(2)) then the constituent directory where the
          file is created depends on the structure of the union: see
          bind(2).

          Since create may succeed even if the file exists, a special
          mechanism is necessary for those applications that require
          an atomic create operation.  If the OEXCL (0x1000) bit is
          set in the mode for a create, the call succeeds only if the
          file does not already exist; see open(5) for details.

          Close closes the file associated with a file descriptor.
          Provided the file descriptor is a valid open descriptor,
          close is guaranteed to close it; there will be no error.
          Files are closed automatically upon termination of a pro-
          cess; close allows the file descriptor to be reused.

     SOURCE
          /sys/src/libc/9syscall

     SEE ALSO
          intro(2), bind(2), stat(2)

     DIAGNOSTICS
          These functions set errstr.