Add lzma_physmem().

I had hoped to keep liblzma as purely a compression
library as possible (e.g. file I/O will go into
a different library), but it seems that applications
linking agaisnt liblzma need some way to determine
the memory usage limit, and knowing the amount of RAM
is one reasonable way to help making such decisions.

Thanks to Jonathan Nieder for the original patch.

3 files changed, 55 insertions, 0 deletions

diff --git a/src/liblzma/api/Makefile.am b/src/liblzma/api/Makefile.am
index 0992d221..4536b0ac 100644
--- a/src/liblzma/api/Makefile.am
+++ b/src/liblzma/api/Makefile.am
@@ -14,6 +14,7 @@ nobase_include_HEADERS = \
 	lzma/container.h \
 	lzma/delta.h \
 	lzma/filter.h \
+	lzma/hardware.h \
 	lzma/index.h \
 	lzma/index_hash.h \
 	lzma/lzma.h \
diff --git a/src/liblzma/api/lzma.h b/src/liblzma/api/lzma.h
index dab29636..f5ab30d1 100644
--- a/src/liblzma/api/lzma.h
+++ b/src/liblzma/api/lzma.h
@@ -308,6 +308,9 @@ extern "C" {
 #include "lzma/index.h"
 #include "lzma/index_hash.h"
 
+/* Hardware information */
+#include "lzma/hardware.h"
+
 /*
  * All subheaders included. Undefine LZMA_H_INTERNAL to prevent applications
  * re-including the subheaders.
diff --git a/src/liblzma/api/lzma/hardware.h b/src/liblzma/api/lzma/hardware.h
new file mode 100644
index 00000000..f44cb602
--- /dev/null
+++ b/src/liblzma/api/lzma/hardware.h
@@ -0,0 +1,51 @@
+/**
+ * \file        lzma/hardware.h
+ * \brief       Hardware information
+ *
+ * Since liblzma can consume a lot of system resources, it also provides
+ * ways to limit the resource usage. Applications linking against liblzma
+ * need to do the actual decisions how much resources to let liblzma to use.
+ * To ease making these decisions, liblzma provides functions to find out
+ * the relevant capabilities of the underlaying hardware. Currently there
+ * is only a function to find out the amount of RAM, but in the future there
+ * will be also a function to detect how many concurrent threads the system
+ * can run.
+ *
+ * \note        On some operating systems, these function may temporarily
+ *              load a shared library or open file descriptor(s) to find out
+ *              the requested hardware information. Unless the application
+ *              assumes that specific file descriptors are not touched by
+ *              other threads, this should have no effect on thread safety.
+ *              Possible operations involving file descriptors will restart
+ *              the syscalls if they return EINTR.
+ */
+
+/*
+ * Author: Lasse Collin
+ *
+ * This file has been put into the public domain.
+ * You can do whatever you want with this file.
+ *
+ * See ../lzma.h for information about liblzma as a whole.
+ */
+
+#ifndef LZMA_H_INTERNAL
+#	error Never include this file directly. Use <lzma.h> instead.
+#endif
+
+
+/**
+ * \brief       Get the total amount of physical memory (RAM) in bytes
+ *
+ * This function may be useful when determining a reasonable memory
+ * usage limit for decompressing or how much memory it is OK to use
+ * for compressing. For example, the default limit used by the xz
+ * command line tool is 40 % of RAM.
+ *
+ * \return      On success, the total amount of physical memory in bytes
+ *              is returned. If the amount of RAM cannot be determined,
+ *              zero is returned. This can happen if an error occurs
+ *              or if there is no code in liblzma to detect the amount
+ *              of RAM on the specific operating system.
+ */
+extern LZMA_API(uint64_t) lzma_physmem(void) lzma_nothrow;