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* $Id: text_mmap.c,v 4.15 2006/11/27 01:52:23 bkorb Exp $
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* Time-stamp: "2006-09-10 14:50:04 bkorb"
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# define MAP_ANONYMOUS MAP_ANON
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* Some weird systems require that a specifically invalid FD number
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* get passed in as an argument value. Which value is that? Well,
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* as everybody knows, if open(2) fails, it returns -1, so that must
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#define AO_INVALID_FD -1
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#define FILE_WRITABLE(_prt,_flg) \
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( (_prt & PROT_WRITE) \
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&& ((_flg & (MAP_SHARED|MAP_PRIVATE)) == MAP_SHARED))
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#define MAP_FAILED_PTR ((void*)MAP_FAILED)
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/*=export_func text_mmap
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* what: map a text file with terminating NUL
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* arg: char const*, pzFile, name of the file to map
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* arg: int, prot, mmap protections (see mmap(2))
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* arg: int, flags, mmap flags (see mmap(2))
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* arg: tmap_info_t*, mapinfo, returned info about the mapping
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* ret-desc: The mmaped data address
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* This routine will mmap a file into memory ensuring that there is at least
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* one @file{NUL} character following the file data. It will return the
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* address where the file contents have been mapped into memory. If there is a
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* problem, then it will return @code{MAP_FAILED} and set @file{errno}
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* The named file does not exist, @code{stat(2)} will set @file{errno} as it
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* will. If the file is not a regular file, @file{errno} will be
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* @code{EINVAL}. At that point, @code{open(2)} is attempted with the access
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* bits set appropriately for the requested @code{mmap(2)} protections and flag
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* bits. On failure, @file{errno} will be set according to the documentation
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* for @code{open(2)}. If @code{mmap(2)} fails, @file{errno} will be set as
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* that routine sets it. If @code{text_mmap} works to this point, a valid
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* address will be returned, but there may still be ``issues''.
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* If the file size is not an even multiple of the system page size, then
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* @code{text_map} will return at this point and @file{errno} will be zero.
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* Otherwise, an anonymous map is attempted. If not available, then an attempt
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* is made to @code{mmap(2)} @file{/dev/zero}. If any of these fail, the
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* address of the file's data is returned, bug @code{no} @file{NUL} characters
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* are mapped after the end of the data.
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* see: mmap(2), open(2), stat(2)
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* err: Any error code issued by mmap(2), open(2), stat(2) is possible.
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* Additionally, if the specified file is not a regular file, then
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* errno will be set to @code{EINVAL}.
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* void* data = text_mmap( "file", PROT_WRITE, MAP_PRIVATE, &mi );
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* if (data == MAP_FAILED) return;
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* no_nul = (mi.txt_size == mi.txt_full_size);
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text_mmap( char const* pzFile, int prot, int flags, tmap_info_t* pMI )
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memset( pMI, 0, sizeof(*pMI) );
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pMI->txt_zero_fd = -1;
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* Make sure we can stat the regular file. Save the file size.
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if (stat( pzFile, &sb ) != 0) {
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pMI->txt_errno = errno;
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return MAP_FAILED_PTR;
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if (! S_ISREG( sb.st_mode )) {
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pMI->txt_errno = errno = EINVAL;
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return MAP_FAILED_PTR;
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pMI->txt_size = sb.st_size;
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* Map mmap flags and protections into open flags and do the open.
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* See if we will be updating the file. If we can alter the memory
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* and if we share the data and we are *not* copy-on-writing the data,
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* then our updates will show in the file, so we must open with
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if (FILE_WRITABLE(prot,flags))
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* If you're not sharing the file and you are writing to it,
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* then don't let anyone else have access to the file.
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if (((flags & MAP_SHARED) == 0) && (prot & PROT_WRITE))
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pMI->txt_fd = open( pzFile, o_flag );
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if (pMI->txt_fd == AO_INVALID_FD) {
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pMI->txt_errno = errno;
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return MAP_FAILED_PTR;
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#ifdef HAVE_MMAP /* * * * * WITH MMAP * * * * * */
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* do the mmap. If we fail, then preserve errno, close the file and
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* return the failure.
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mmap(NULL, pMI->txt_size+1, prot, flags, pMI->txt_fd, (size_t)0);
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if (pMI->txt_data == MAP_FAILED_PTR) {
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pMI->txt_errno = errno;
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* Most likely, everything will turn out fine now. The only difficult
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* part at this point is coping with files with sizes that are a multiple
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* of the page size. Handling that is what this whole thing is about.
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pMI->txt_zero_fd = -1;
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size_t pgsz = sysconf(_SC_PAGESIZE);
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size_t pgsz = getpagesize();
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* Compute the pagesize rounded mapped memory size.
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* IF this is not the same as the file size, then there are NUL's
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* at the end of the file mapping and all is okay.
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pMI->txt_full_size = (pMI->txt_size + (pgsz - 1)) & ~(pgsz - 1);
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if (pMI->txt_size != pMI->txt_full_size)
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return pMI->txt_data;
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* Still here? We have to remap the trailing inaccessible page
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* either anonymously or to /dev/zero.
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pMI->txt_full_size += pgsz;
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#if defined(MAP_ANONYMOUS)
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(void*)(((char*)pMI->txt_data) + pMI->txt_size),
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pgsz, PROT_READ|PROT_WRITE,
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MAP_ANONYMOUS|MAP_FIXED|MAP_PRIVATE, AO_INVALID_FD, (size_t)0);
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if (pNuls != MAP_FAILED_PTR)
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return pMI->txt_data;
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pMI->txt_errno = errno;
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#elif defined(HAVE_DEV_ZERO)
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pMI->txt_zero_fd = open( "/dev/zero", O_RDONLY );
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if (pMI->txt_zero_fd == AO_INVALID_FD) {
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pMI->txt_errno = errno;
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(void*)(((char*)pMI->txt_data) + pMI->txt_size), pgsz,
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PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED,
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pMI->txt_zero_fd, 0 );
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if (pNuls != MAP_FAILED_PTR)
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return pMI->txt_data;
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pMI->txt_errno = errno;
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close( pMI->txt_zero_fd );
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pMI->txt_zero_fd = -1;
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pMI->txt_full_size = pMI->txt_size;
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void* p = AGALOC( pMI->txt_size+1, "file text" );
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memcpy( p, pMI->txt_data, pMI->txt_size );
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((char*)p)[pMI->txt_size] = NUL;
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munmap(pMI->txt_data, pMI->txt_size );
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return pMI->txt_data;
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#else /* * * * * * no HAVE_MMAP * * * * * */
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pMI->txt_data = AGALOC( pMI->txt_size+1, "file text" );
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if (pMI->txt_data == NULL) {
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pMI->txt_errno = ENOMEM;
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size_t sz = pMI->txt_size;
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char* pz = pMI->txt_data;
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ssize_t rdct = read( pMI->txt_fd, pz, sz );
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pMI->txt_errno = errno;
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fprintf( stderr, zFSErrReadFile,
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errno, strerror( errno ), pzFile );
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free( pMI->txt_data );
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* We never need a dummy page mapped in
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pMI->txt_zero_fd = -1;
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return pMI->txt_data;
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#endif /* * * * * * no HAVE_MMAP * * * * * */
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if (pMI->txt_fd >= 0) {
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close( pMI->txt_fd );
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errno = pMI->txt_errno;
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pMI->txt_data = MAP_FAILED_PTR;
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return pMI->txt_data;
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/*=export_func text_munmap
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* what: unmap the data mapped in by text_mmap
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* arg: tmap_info_t*, mapinfo, info about the mapping
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* ret-desc: -1 or 0. @file{errno} will have the error code.
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* This routine will unmap the data mapped in with @code{text_mmap} and close
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* the associated file descriptors opened by that function.
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* see: munmap(2), close(2)
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* err: Any error code issued by munmap(2) or close(2) is possible.
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text_munmap( tmap_info_t* pMI )
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if (pMI->txt_alloc) {
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* IF the user has write permission and the text is not mapped private,
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* then write back any changes. Hopefully, nobody else has modified
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* the file in the mean time.
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if ( ((pMI->txt_prot & PROT_WRITE) != 0)
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&& ((pMI->txt_flags & MAP_PRIVATE) == 0)) {
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if (lseek(pMI->txt_fd, (size_t)0, SEEK_SET) != 0)
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res = (write( pMI->txt_fd, pMI->txt_data, pMI->txt_size ) < 0)
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AGFREE( pMI->txt_data );
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res = munmap( pMI->txt_data, pMI->txt_full_size );
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res = close( pMI->txt_fd );
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if (pMI->txt_zero_fd != -1) {
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res = close( pMI->txt_zero_fd );
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pMI->txt_zero_fd = -1;
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pMI->txt_errno = errno;
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#else /* HAVE_MMAP */
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* IF the memory is writable *AND* it is not private (copy-on-write)
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* *AND* the memory is "sharable" (seen by other processes)
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* THEN rewrite the data.
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if ( FILE_WRITABLE(pMI->txt_prot, pMI->txt_flags)
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&& (lseek( pMI->txt_fd, 0, SEEK_SET ) >= 0) ) {
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write( pMI->txt_fd, pMI->txt_data, pMI->txt_size );
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close( pMI->txt_fd );
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pMI->txt_errno = errno;
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free( pMI->txt_data );
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return pMI->txt_errno;
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#endif /* HAVE_MMAP */
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* c-file-style: "stroustrup"
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* indent-tabs-mode: nil
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* end of autoopts/text_mmap.c */
added
removed
libopts/text_mmap.c
