Fix statfs(2) for 32-bit user space

config/kernel-in-compat-syscall.m4

@@ -0,0 +1,20 @@
+dnl #
+dnl # 4.5 API change
+dnl # Added in_compat_syscall() which can be overridden on a per-
+dnl # architecture basis.  Prior to this is_compat_task() was the
+dnl # provided interface.
+dnl #
+AC_DEFUN([ZFS_AC_KERNEL_IN_COMPAT_SYSCALL], [
+	AC_MSG_CHECKING([whether in_compat_syscall() is available])
+	ZFS_LINUX_TRY_COMPILE([
+		#include <linux/compat.h>
+	],[
+		in_compat_syscall();
+	],[
+		AC_MSG_RESULT(yes)
+		AC_DEFINE(HAVE_IN_COMPAT_SYSCALL, 1,
+		    [in_compat_syscall() is available])
+	],[
+		AC_MSG_RESULT(no)
+	])
+])

config/kernel.m4

@@ -160,6 +160,7 @@ AC_DEFUN([ZFS_AC_CONFIG_KERNEL], [
 	ZFS_AC_KERNEL_GLOBAL_PAGE_STATE
 	ZFS_AC_KERNEL_ACL_HAS_REFCOUNT
 	ZFS_AC_KERNEL_USERNS_CAPABILITIES
+	ZFS_AC_KERNEL_IN_COMPAT_SYSCALL
 
 	AS_IF([test "$LINUX_OBJ" != "$LINUX"], [
 		KERNEL_MAKE="$KERNEL_MAKE O=$LINUX_OBJ"

include/linux/vfs_compat.h

@@ -30,6 +30,7 @@
 #include <sys/taskq.h>
 #include <sys/cred.h>
 #include <linux/backing-dev.h>
+#include <linux/compat.h>
 
 /*
  * 2.6.28 API change,
@@ -626,4 +627,21 @@ inode_set_iversion(struct inode *ip, u64 val)
 }
 #endif
 
+/*
+ * Returns true when called in the context of a 32-bit system call.
+ */
+static inline int
+zpl_is_32bit_api(void)
+{
+#ifdef CONFIG_COMPAT
+#ifdef HAVE_IN_COMPAT_SYSCALL
+	return (in_compat_syscall());
+#else
+	return (is_compat_task());
+#endif
+#else
+	return (BITS_PER_LONG == 32);
+#endif
+}
+
 #endif /* _ZFS_VFS_H */

module/zfs/zfs_vfsops.c

@@ -1422,16 +1422,14 @@ zfs_statvfs(struct dentry *dentry, struct kstatfs *statp)
 {
 	zfsvfs_t *zfsvfs = dentry->d_sb->s_fs_info;
 	uint64_t refdbytes, availbytes, usedobjs, availobjs;
-	uint64_t fsid;
-	uint32_t bshift;
 	int err = 0;
 
 	ZFS_ENTER(zfsvfs);
 
 	dmu_objset_space(zfsvfs->z_os,
 	    &refdbytes, &availbytes, &usedobjs, &availobjs);
 
-	fsid = dmu_objset_fsid_guid(zfsvfs->z_os);
+	uint64_t fsid = dmu_objset_fsid_guid(zfsvfs->z_os);
 	/*
 	 * The underlying storage pool actually uses multiple block
 	 * size.  Under Solaris frsize (fragment size) is reported as
@@ -1443,7 +1441,7 @@ zfs_statvfs(struct dentry *dentry, struct kstatfs *statp)
 	 */
 	statp->f_frsize = zfsvfs->z_max_blksz;
 	statp->f_bsize = zfsvfs->z_max_blksz;
-	bshift = fls(statp->f_bsize) - 1;
+	uint32_t bshift = fls(statp->f_bsize) - 1;
 
 	/*
 	 * The following report "total" blocks of various kinds in
@@ -1460,7 +1458,7 @@ zfs_statvfs(struct dentry *dentry, struct kstatfs *statp)
 	 * static metadata.  ZFS doesn't preallocate files, so the best
 	 * we can do is report the max that could possibly fit in f_files,
 	 * and that minus the number actually used in f_ffree.
-	 * For f_ffree, report the smaller of the number of object available
+	 * For f_ffree, report the smaller of the number of objects available
 	 * and the number of blocks (each object will take at least a block).
 	 */
 	statp->f_ffree = MIN(availobjs, availbytes >> DNODE_SHIFT);

module/zfs/zpl_super.c

@@ -181,6 +181,28 @@ zpl_statfs(struct dentry *dentry, struct kstatfs *statp)
 	spl_fstrans_unmark(cookie);
 	ASSERT3S(error, <=, 0);
 
+	/*
+	 * If required by a 32-bit system call, dynamically scale the
+	 * block size up to 16MiB and decrease the block counts.  This
+	 * allows for a maximum size of 64EiB to be reported.  The file
+	 * counts must be artificially capped at 2^32-1.
+	 */
+	if (unlikely(zpl_is_32bit_api())) {
+		while (statp->f_blocks > UINT32_MAX &&
+		    statp->f_bsize < SPA_MAXBLOCKSIZE) {
+			statp->f_frsize <<= 1;
+			statp->f_bsize <<= 1;
+
+			statp->f_blocks >>= 1;
+			statp->f_bfree >>= 1;
+			statp->f_bavail >>= 1;
+		}
+
+		uint64_t usedobjs = statp->f_files - statp->f_ffree;
+		statp->f_ffree = MIN(statp->f_ffree, UINT32_MAX - usedobjs);
+		statp->f_files = statp->f_ffree + usedobjs;
+	}
+
 	return (error);
 }