zstd: Implement core detection (#2083)

The bsdtar manual page claims that setting zstd:threads to 0 tells zstd
to use as many threads as there are cores in the system, but it actually
disables multi-threading.  Replace 0 with the number of configured
processors.

While here, add a previously missing overflow check.

Co-authored-by: Martin Matuska <martin@matuska.de>

CMakeLists.txt

@@ -1497,6 +1497,7 @@ CHECK_FUNCTION_EXISTS_GLIBC(strncpy_s HAVE_STRNCPY_S)
 CHECK_FUNCTION_EXISTS_GLIBC(strnlen HAVE_STRNLEN)
 CHECK_FUNCTION_EXISTS_GLIBC(strrchr HAVE_STRRCHR)
 CHECK_FUNCTION_EXISTS_GLIBC(symlink HAVE_SYMLINK)
+CHECK_FUNCTION_EXISTS_GLIBC(sysconf HAVE_SYSCONF)
 CHECK_FUNCTION_EXISTS_GLIBC(timegm HAVE_TIMEGM)
 CHECK_FUNCTION_EXISTS_GLIBC(tzset HAVE_TZSET)
 CHECK_FUNCTION_EXISTS_GLIBC(unlinkat HAVE_UNLINKAT)

build/cmake/config.h.in

@@ -1094,6 +1094,9 @@ typedef uint64_t uintmax_t;
 /* Define to 1 if you have the `symlink' function. */
 #cmakedefine HAVE_SYMLINK 1
 
+/* Define to 1 if you have the `sysconf' function. */
+#cmakedefine HAVE_SYSCONF 1
+
 /* Define to 1 if you have the <sys/acl.h> header file. */
 #cmakedefine HAVE_SYS_ACL_H 1
 

configure.ac

@@ -804,6 +804,7 @@ AC_CHECK_FUNCS([nl_langinfo openat pipe poll posix_spawnp readlink readlinkat])
 AC_CHECK_FUNCS([readpassphrase])
 AC_CHECK_FUNCS([select setenv setlocale sigaction statfs statvfs])
 AC_CHECK_FUNCS([strchr strdup strerror strncpy_s strnlen strrchr symlink])
+AC_CHECK_FUNCS([sysconf])
 AC_CHECK_FUNCS([timegm tzset unlinkat unsetenv utime utimensat utimes vfork])
 AC_CHECK_FUNCS([wcrtomb wcscmp wcscpy wcslen wctomb wmemcmp wmemcpy wmemmove])
 AC_CHECK_FUNCS([_fseeki64 _get_timezone])

libarchive/archive_write_add_filter_zstd.c

@@ -29,6 +29,9 @@
 #ifdef HAVE_ERRNO_H
 #include <errno.h>
 #endif
+#ifdef HAVE_LIMITS_H
+#include <limits.h>
+#endif
 #ifdef HAVE_STDINT_H
 #include <stdint.h>
 #endif
@@ -38,6 +41,9 @@
 #ifdef HAVE_STRING_H
 #include <string.h>
 #endif
+#ifdef HAVE_UNISTD_H
+#include <unistd.h>
+#endif
 #ifdef HAVE_ZSTD_H
 #include <zstd.h>
 #endif
@@ -266,7 +272,13 @@ archive_compressor_zstd_options(struct archive_write_filter *f, const char *key,
 		if (string_to_number(value, &threads) != ARCHIVE_OK) {
 			return (ARCHIVE_WARN);
 		}
-		if (threads < 0) {
+
+#if defined(HAVE_SYSCONF) && defined(_SC_NPROCESSORS_ONLN)
+		if (threads == 0) {
+			threads = sysconf(_SC_NPROCESSORS_ONLN);
+		}
+#endif
+		if (threads < 0 || threads > INT_MAX) {
 			return (ARCHIVE_WARN);
 		}
 		data->threads = (int)threads;

tar/bsdtar.1

@@ -23,7 +23,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd March 1, 2024
+.Dd April 23, 2024
 .Dt TAR 1
 .Os
 .Sh NAME
@@ -644,14 +644,13 @@ A decimal integer from 4 to 7 specifying the lz4 compression block size
 .It Cm lz4:block-dependence
 Use the previous block of the block being compressed for
 a compression dictionary to improve compression ratio.
-.It Cm zstd:compression-level
-A decimal integer specifying the zstd compression level. Supported values depend
+.It Cm zstd:compression-level Ns = Ns Ar N
+A decimal integer specifying the zstd compression level.
+Supported values depend
 on the library version, common values are from 1 to 22.
-.It Cm zstd:threads
-Specify the number of worker threads to use.
-Setting threads to a special value 0 makes
-.Xr zstd 1
-use as many threads as there are CPU cores on the system.
+.It Cm zstd:threads Ns = Ns Ar N
+Specify the number of worker threads to use, or 0 to use as many
+threads as there are CPU cores in the system.
 .It Cm zstd:frame-per-file
 Start a new compression frame at the beginning of each file in the
 archive.