libxfs: implement get_random_u32

Actually query the kernel for some random bytes instead of returning
zero, if that's possible.  The most noticeable effect of this is that
mkfs will now create the rtbitmap file, the rtsummary file, and children
of the root directory with a nonzero generation.  Apparently xfsdump
requires that the root directory have a generation number of zero.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>

diff --git a/configure.ac b/configure.ac
index d021c519d5383e22768550c263fb41fe926f5d43..1c9fa817379f67b9c12642afb8575395f600f27b 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -152,6 +152,7 @@ AC_HAVE_DEVMAPPER
 AC_HAVE_MALLINFO
 AC_HAVE_MALLINFO2
 AC_HAVE_MEMFD_CREATE
+AC_HAVE_GETRANDOM_NONBLOCK
 if test "$enable_scrub" = "yes"; then
         if test "$enable_libicu" = "yes" || test "$enable_libicu" = "probe"; then
                 AC_HAVE_LIBICU

diff --git a/include/builddefs.in b/include/builddefs.in
index 07c4a43f78a01c7c1783c5e4bde58741360a1c96..c8c7de7fd2fd38617dbdba5321dd6feb42105b1f 100644 (file)
--- a/include/builddefs.in
+++ b/include/builddefs.in
@@ -102,6 +102,7 @@ HAVE_DEVMAPPER = @have_devmapper@
 HAVE_MALLINFO = @have_mallinfo@
 HAVE_MALLINFO2 = @have_mallinfo2@
 HAVE_MEMFD_CREATE = @have_memfd_create@
+HAVE_GETRANDOM_NONBLOCK = @have_getrandom_nonblock@
 HAVE_LIBICU = @have_libicu@
 HAVE_SYSTEMD = @have_systemd@
 SYSTEMD_SYSTEM_UNIT_DIR = @systemd_system_unit_dir@

diff --git a/libxfs/Makefile b/libxfs/Makefile
index 8c93d7b539fb73e9a178a49bacd2a2ca0e479a32..fd623cf40c0047cdf7fc9203074a6cd2c189cdf1 100644 (file)
--- a/libxfs/Makefile
+++ b/libxfs/Makefile
@@ -135,6 +135,10 @@ ifeq ($(HAVE_MEMFD_CREATE),yes)
 LCFLAGS += -DHAVE_MEMFD_CREATE
 endif
 
+ifeq ($(HAVE_GETRANDOM_NONBLOCK),yes)
+LCFLAGS += -DHAVE_GETRANDOM_NONBLOCK
+endif
+
 FCFLAGS = -I.
 
 LTLIBS = $(LIBPTHREAD) $(LIBRT)

diff --git a/libxfs/libxfs_priv.h b/libxfs/libxfs_priv.h
index ecacfff82d722b948e39459383f5fb5d535ed777..8dd364b0da914ad36a91a0df5fb29b7cf04729ac 100644 (file)
--- a/libxfs/libxfs_priv.h
+++ b/libxfs/libxfs_priv.h
@@ -63,6 +63,9 @@
 #include "libfrog/crc32c.h"
 
 #include <sys/xattr.h>
+#ifdef HAVE_GETRANDOM_NONBLOCK
+#include <sys/random.h>
+#endif
 
 /* Zones used in libxfs allocations that aren't in shared header files */
 extern struct kmem_cache *xfs_buf_item_cache;
@@ -212,11 +215,11 @@ static inline bool WARN_ON(bool expr) {
 #define percpu_counter_read_positive(x)        ((*x) > 0 ? (*x) : 0)
 #define percpu_counter_sum_positive(x) ((*x) > 0 ? (*x) : 0)
 
-/*
- * get_random_u32 is used for di_gen inode allocation, it must be zero for
- * libxfs or all sorts of badness can occur!
- */
+#ifdef HAVE_GETRANDOM_NONBLOCK
+uint32_t get_random_u32(void);
+#else
 #define get_random_u32()       (0)
+#endif
 
 #define PAGE_SIZE              getpagesize()
 

diff --git a/libxfs/util.c b/libxfs/util.c
index 7aa92c0e4a66a9c2cc2bd56e6e71cd98cf7dbac9..a3f3ad299336c7c57d427ea41c7058e91777da60 100644 (file)
--- a/libxfs/util.c
+++ b/libxfs/util.c
@@ -462,3 +462,22 @@ void xfs_dirattr_mark_sick(struct xfs_inode *ip, int whichfork) { }
 void xfs_da_mark_sick(struct xfs_da_args *args) { }
 void xfs_inode_mark_sick(struct xfs_inode *ip, unsigned int mask) { }
 void xfs_rt_mark_sick(struct xfs_mount *mp, unsigned int mask) { }
+
+#ifdef HAVE_GETRANDOM_NONBLOCK
+uint32_t
+get_random_u32(void)
+{
+       uint32_t        ret;
+       ssize_t         sz;
+
+       /*
+        * Try to extract a u32 of randomness from /dev/urandom.  If that
+        * fails, fall back to returning zero like we used to do.
+        */
+       sz = getrandom(&ret, sizeof(ret), GRND_NONBLOCK);
+       if (sz != sizeof(ret))
+               return 0;
+
+       return ret;
+}
+#endif

diff --git a/m4/package_libcdev.m4 b/m4/package_libcdev.m4
index 6de8b33ee29fd5c3018f1ba8cc6d4b9d7024c190..13cb5156d794f7849ac82f61df23e203570a94f1 100644 (file)
--- a/m4/package_libcdev.m4
+++ b/m4/package_libcdev.m4
@@ -195,6 +195,21 @@ memfd_create(0, 0);
     AC_SUBST(have_memfd_create)
   ])
 
+#
+# Check if we have a getrandom syscall with a GRND_NONBLOCK flag
+#
+AC_DEFUN([AC_HAVE_GETRANDOM_NONBLOCK],
+  [ AC_MSG_CHECKING([for getrandom and GRND_NONBLOCK])
+    AC_LINK_IFELSE([AC_LANG_PROGRAM([[
+#include <sys/random.h>
+    ]], [[
+         unsigned int moo;
+         return getrandom(&moo, sizeof(moo), GRND_NONBLOCK);
+    ]])],[have_getrandom_nonblock=yes
+       AC_MSG_RESULT(yes)],[AC_MSG_RESULT(no)])
+    AC_SUBST(have_getrandom_nonblock)
+  ])
+
 AC_DEFUN([AC_PACKAGE_CHECK_LTO],
   [ AC_MSG_CHECKING([if C compiler supports LTO])
     OLD_CFLAGS="$CFLAGS"

diff --git a/mkfs/proto.c b/mkfs/proto.c
index 58edc59f7152cdff00a0959991dfd72a877e9dd2..96cb9f8544bf853adf5228cc736992750fcf1c34 100644 (file)
--- a/mkfs/proto.c
+++ b/mkfs/proto.c
@@ -462,6 +462,9 @@ creatproto(
                                                        fsx->fsx_xflags);
                        ip->i_cowextsize = fsx->fsx_cowextsize;
                }
+
+               /* xfsdump breaks if the root dir has a nonzero generation */
+               inode->i_generation = 0;
        }
 
        libxfs_trans_log_inode(*tpp, ip, XFS_ILOG_CORE);