Precaution to access user mode buffers from kernel

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fclose

FCLOSE(3)						     Linux Programmer's Manual							 FCLOSE(3)

NAME

       fclose - close a stream

SYNOPSIS

       #include <stdio.h>

       int fclose(FILE *fp);

DESCRIPTION

       The fclose() function will flushes the stream pointed to by fp (writing any buffered output data using fflush(3)) and closes the underlying
       file descriptor.

RETURN VALUE

       Upon successful completion 0 is returned.  Otherwise, EOF is returned and errno is set to indicate the error.  In either case  any  further
       access (including another call to fclose()) to the stream results in undefined behavior.

ERRORS

       EBADF  The file descriptor underlying fp is not valid.

       The fclose() function may also fail and set errno for any of the errors specified for the routines close(2), write(2) or fflush(3).

CONFORMING TO

       C89, C99.

NOTES

       Note that fclose() only flushes the user space buffers provided by the C library.  To ensure that the data is physically stored on disk the
       kernel buffers must be flushed too, for example, with sync(2) or fsync(2).

SEE ALSO

       close(2), fcloseall(3), fflush(3), fopen(3), setbuf(3)

COLOPHON

       This page is part of release 3.25 of the Linux man-pages project.  A description of the project, and information about reporting bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.

GNU
								    2009-02-23								 FCLOSE(3)

UNIX for Advanced & Expert Users