/* $NetBSD: text_mmap.c,v 1.5 2020/05/25 20:47:35 christos Exp $ */
/**
* @file text_mmap.c
*
* Map a text file, ensuring the text always has an ending NUL byte.
*
* @addtogroup autoopts
* @{
*/
/*
* This file is part of AutoOpts, a companion to AutoGen.
* AutoOpts is free software.
* AutoOpts is Copyright (C) 1992-2015 by Bruce Korb - all rights reserved
*
* AutoOpts is available under any one of two licenses. The license
* in use must be one of these two and the choice is under the control
* of the user of the license.
*
* The GNU Lesser General Public License, version 3 or later
* See the files "COPYING.lgplv3" and "COPYING.gplv3"
*
* The Modified Berkeley Software Distribution License
* See the file "COPYING.mbsd"
*
* These files have the following sha256 sums:
*
* 8584710e9b04216a394078dc156b781d0b47e1729104d666658aecef8ee32e95 COPYING.gplv3
* 4379e7444a0e2ce2b12dd6f5a52a27a4d02d39d247901d3285c88cf0d37f477b COPYING.lgplv3
* 13aa749a5b0a454917a944ed8fffc530b784f5ead522b1aacaf4ec8aa55a6239 COPYING.mbsd
*/
#if defined(HAVE_MMAP)
# ifndef MAP_ANONYMOUS
# ifdef MAP_ANON
# define MAP_ANONYMOUS MAP_ANON
# endif
# endif
# if ! defined(MAP_ANONYMOUS) && ! defined(HAVE_DEV_ZERO)
/*
* We must have either /dev/zero or anonymous mapping for
* this to work.
*/
# undef HAVE_MMAP
# else
# ifdef _SC_PAGESIZE
# define GETPAGESIZE() sysconf(_SC_PAGESIZE)
# else
# define GETPAGESIZE() getpagesize()
# endif
# endif
#endif
/*
* Some weird systems require that a specifically invalid FD number
* get passed in as an argument value. Which value is that? Well,
* as everybody knows, if open(2) fails, it returns -1, so that must
* be the value. :)
*/
#define AO_INVALID_FD -1
#define FILE_WRITABLE(_prt,_flg) \
( (_prt & PROT_WRITE) \
&& ((_flg & (MAP_SHARED|MAP_PRIVATE)) == MAP_SHARED))
#define MAP_FAILED_PTR (VOIDP(MAP_FAILED))
/**
* Load the contents of a text file. There are two separate implementations,
* depending up on whether mmap(3) is available.
*
* If not available, malloc the file length plus one byte. Read it in
* and NUL terminate.
*
* If available, first check to see if the text file size is a multiple of a
* page size. If it is, map the file size plus an extra page from either
* anonymous memory or from /dev/zero. Then map the file text on top of the
* first pages of the anonymous/zero pages. Otherwise, just map the file
* because there will be NUL bytes provided at the end.
*
* @param mapinfo a structure holding everything we need to know
* about the mapping.
*
* @param pzFile name of the file, for error reporting.
*/
static void
load_text_file(tmap_info_t * mapinfo, char const * pzFile)
{
#if ! defined(HAVE_MMAP)
mapinfo->txt_data = AGALOC(mapinfo->txt_size+1, "file text");
if (mapinfo->txt_data == NULL) {
mapinfo->txt_errno = ENOMEM;
return;
}
{
size_t sz = mapinfo->txt_size;
char * pz = mapinfo->txt_data;
while (sz > 0) {
ssize_t rdct = read(mapinfo->txt_fd, pz, sz);
if (rdct <= 0) {
mapinfo->txt_errno = errno;
fserr_warn("libopts", "read", pzFile);
free(mapinfo->txt_data);
return;
}
pz += rdct;
sz -= rdct;
}
*pz = NUL;
}
mapinfo->txt_errno = 0;
#else /* HAVE mmap */
size_t const pgsz = (size_t)GETPAGESIZE();
void * map_addr = NULL;
(void)pzFile;
mapinfo->txt_full_size = (mapinfo->txt_size + pgsz) & ~(pgsz - 1);
if (mapinfo->txt_full_size == (mapinfo->txt_size + pgsz)) {
/*
* The text is a multiple of a page boundary. We must map an
* extra page so the text ends with a NUL.
*/
#if defined(MAP_ANONYMOUS)
map_addr = mmap(NULL, mapinfo->txt_full_size, PROT_READ|PROT_WRITE,
MAP_ANONYMOUS|MAP_PRIVATE, AO_INVALID_FD, 0);
#else
mapinfo->txt_zero_fd = open("/dev/zero", O_RDONLY);
if (mapinfo->txt_zero_fd == AO_INVALID_FD) {
mapinfo->txt_errno = errno;
return;
}
map_addr = mmap(NULL, mapinfo->txt_full_size, PROT_READ|PROT_WRITE,
MAP_PRIVATE, mapinfo->txt_zero_fd, 0);
#endif
if (map_addr == MAP_FAILED_PTR) {
mapinfo->txt_errno = errno;
return;
}
mapinfo->txt_flags |= MAP_FIXED;
}
mapinfo->txt_data =
mmap(map_addr, mapinfo->txt_size, mapinfo->txt_prot,
mapinfo->txt_flags, mapinfo->txt_fd, 0);
if (mapinfo->txt_data == MAP_FAILED_PTR)
mapinfo->txt_errno = errno;
#endif /* HAVE_MMAP */
}
/**
* Make sure all the parameters are correct: we have a file name that
* is a text file that we can read.
*
* @param fname the text file to map
* @param prot the memory protections requested (read/write/etc.)
* @param flags mmap flags
* @param mapinfo a structure holding everything we need to know
* about the mapping.
*/
static void
validate_mmap(char const * fname, int prot, int flags, tmap_info_t * mapinfo)
{
memset(mapinfo, 0, sizeof(*mapinfo));
#if defined(HAVE_MMAP) && ! defined(MAP_ANONYMOUS)
mapinfo->txt_zero_fd = AO_INVALID_FD;
#endif
mapinfo->txt_fd = AO_INVALID_FD;
mapinfo->txt_prot = prot;
mapinfo->txt_flags = flags;
/*
* Map mmap flags and protections into open flags and do the open.
*/
{
/*
* See if we will be updating the file. If we can alter the memory
* and if we share the data and we are *not* copy-on-writing the data,
* then our updates will show in the file, so we must open with
* write access.
*/
int o_flag = FILE_WRITABLE(prot, flags) ? O_RDWR : O_RDONLY;
/*
* If you're not sharing the file and you are writing to it,
* then don't let anyone else have access to the file.
*/
if (((flags & MAP_SHARED) == 0) && (prot & PROT_WRITE))
o_flag |= O_EXCL;
mapinfo->txt_fd = open(fname, o_flag);
if (mapinfo->txt_fd < 0) {
mapinfo->txt_errno = errno;
mapinfo->txt_fd = AO_INVALID_FD;
return;
}
}
/*
* Make sure we can stat the regular file. Save the file size.
*/
{
struct stat sb;
if (fstat(mapinfo->txt_fd, &sb) != 0) {
mapinfo->txt_errno = errno;
close(mapinfo->txt_fd);
return;
}
if (! S_ISREG(sb.st_mode)) {
mapinfo->txt_errno = errno = EINVAL;
close(mapinfo->txt_fd);
return;
}
mapinfo->txt_size = (size_t)sb.st_size;
}
if (mapinfo->txt_fd == AO_INVALID_FD)
mapinfo->txt_errno = errno;
}
/**
* Close any files opened by the mapping.
*
* @param mi a structure holding everything we need to know about the map.
*/
static void
close_mmap_files(tmap_info_t * mi)
{
if (mi->txt_fd == AO_INVALID_FD)
return;
close(mi->txt_fd);
mi->txt_fd = AO_INVALID_FD;
#if defined(HAVE_MMAP) && ! defined(MAP_ANONYMOUS)
if (mi->txt_zero_fd == AO_INVALID_FD)
return;
close(mi->txt_zero_fd);
mi->txt_zero_fd = AO_INVALID_FD;
#endif
}
/*=export_func text_mmap
* private:
*
* what: map a text file with terminating NUL
*
* arg: char const *, pzFile, name of the file to map
* arg: int, prot, mmap protections (see mmap(2))
* arg: int, flags, mmap flags (see mmap(2))
* arg: tmap_info_t *, mapinfo, returned info about the mapping
*
* ret-type: void *
* ret-desc: The mmaped data address
*
* doc:
*
* This routine will mmap a file into memory ensuring that there is at least
* one @file{NUL} character following the file data. It will return the
* address where the file contents have been mapped into memory. If there is a
* problem, then it will return @code{MAP_FAILED} and set @code{errno}
* appropriately.
*
* The named file does not exist, @code{stat(2)} will set @code{errno} as it
* will. If the file is not a regular file, @code{errno} will be
* @code{EINVAL}. At that point, @code{open(2)} is attempted with the access
* bits set appropriately for the requested @code{mmap(2)} protections and flag
* bits. On failure, @code{errno} will be set according to the documentation
* for @code{open(2)}. If @code{mmap(2)} fails, @code{errno} will be set as
* that routine sets it. If @code{text_mmap} works to this point, a valid
* address will be returned, but there may still be ``issues''.
*
* If the file size is not an even multiple of the system page size, then
* @code{text_map} will return at this point and @code{errno} will be zero.
* Otherwise, an anonymous map is attempted. If not available, then an attempt
* is made to @code{mmap(2)} @file{/dev/zero}. If any of these fail, the
* address of the file's data is returned, bug @code{no} @file{NUL} characters
* are mapped after the end of the data.
*
* see: mmap(2), open(2), stat(2)
*
* err: Any error code issued by mmap(2), open(2), stat(2) is possible.
* Additionally, if the specified file is not a regular file, then
* errno will be set to @code{EINVAL}.
*
* example:
* #include <mylib.h>
* tmap_info_t mi;
* int no_nul;
* void * data = text_mmap("file", PROT_WRITE, MAP_PRIVATE, &mi);
* if (data == MAP_FAILED) return;
* no_nul = (mi.txt_size == mi.txt_full_size);
* << use the data >>
* text_munmap(&mi);
=*/
void *
text_mmap(char const * pzFile, int prot, int flags, tmap_info_t * mi)
{
validate_mmap(pzFile, prot, flags, mi);
if (mi->txt_errno != 0)
return MAP_FAILED_PTR;
load_text_file(mi, pzFile);
if (mi->txt_errno == 0)
return mi->txt_data;
close_mmap_files(mi);
errno = mi->txt_errno;
mi->txt_data = MAP_FAILED_PTR;
return mi->txt_data;
}
/*=export_func text_munmap
* private:
*
* what: unmap the data mapped in by text_mmap
*
* arg: tmap_info_t *, mapinfo, info about the mapping
*
* ret-type: int
* ret-desc: -1 or 0. @code{errno} will have the error code.
*
* doc:
*
* This routine will unmap the data mapped in with @code{text_mmap} and close
* the associated file descriptors opened by that function.
*
* see: munmap(2), close(2)
*
* err: Any error code issued by munmap(2) or close(2) is possible.
=*/
int
text_munmap(tmap_info_t * mi)
{
errno = 0;
#ifdef HAVE_MMAP
(void)munmap(mi->txt_data, mi->txt_full_size);
#else /* don't HAVE_MMAP */
/*
* IF the memory is writable *AND* it is not private (copy-on-write)
* *AND* the memory is "sharable" (seen by other processes)
* THEN rewrite the data. Emulate mmap visibility.
*/
if ( FILE_WRITABLE(mi->txt_prot, mi->txt_flags)
&& (lseek(mi->txt_fd, 0, SEEK_SET) >= 0) ) {
write(mi->txt_fd, mi->txt_data, mi->txt_size);
}
free(mi->txt_data);
#endif /* HAVE_MMAP */
mi->txt_errno = errno;
close_mmap_files(mi);
return mi->txt_errno;
}
/** @}
*
* Local Variables:
* mode: C
* c-file-style: "stroustrup"
* indent-tabs-mode: nil
* End:
* end of autoopts/text_mmap.c */