open.2, sync_file_range.2, umount.2: Global fix: s/filesystem/file system/

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man2/open.2

@@ -680,7 +680,7 @@ and
 .B O_RSYNC
 to the same numerical value as
 .BR O_SYNC
-Most Linux filesystems don't actually implement the POSIX
+Most Linux file systems don't actually implement the POSIX
 .B O_SYNC
 semantics, which require all metadata updates of a write
 to be on disk on returning to userspace, but only the

man2/sync_file_range.2

@@ -88,11 +88,11 @@ Therefore, unless the application is strictly performing overwrites of
 already-instantiated disk blocks, there are no guarantees that the data will
 be available after a crash.
 There is no user interface to know if a write is purely an overwrite.
-On filesystem using copy-on-write semantics (e.g.,
+On file systems using copy-on-write semantics (e.g.,
 .IR btrfs )
 an overwrite of existing allocated blocks is impossible.
 When writing into preallocated space,
-many filesystems also require calls into the block
+many file systems also require calls into the block
 allocator, which this system call does not sync out to disk.
 This system call does not flush disk write caches and thus does not provide
 any data integrity on systems with volatile disk write caches.

man2/umount.2

@@ -94,9 +94,9 @@ On error, \-1 is returned, and
 .I errno
 is set appropriately.
 .SH ERRORS
-The error values given below result from filesystem type independent
+The error values given below result from file-system type independent
 errors.
-Each filesystem type may have its own special errors and its
+Each file system type may have its own special errors and its
 own special behavior.
 See the kernel source code for details.
 .TP