Add detailed documentation about lock files

* doc/emacs/files.texi (Interlocking): Point user at detailed
file locking description in lisp reference manual.  Add index
entry for '.#' to improve disoverability of information about locking.

* doc/lispref/files.texi (File Locks): Describe in detail what
the form of the lock file is.  Add index entry for '.#' to
improve disoverability of information about locking.

* src/filelock.c (create-lockfiles): Add cross reference to
file locking in user manual and to 'lock-buffer'.  Add string
'.#' to help users find the doc string.

1 files changed, 12 insertions, 2 deletions

diff --git a/doc/lispref/files.texi b/doc/lispref/files.texi
index 5137f3a9ab4..6dfca0f2128 100644
--- a/doc/lispref/files.texi
+++ b/doc/lispref/files.texi
@@ -712,6 +712,7 @@ with-temp-buffer,, The Current Buffer}.
 @section File Locks
 @cindex file locks
 @cindex lock file
+@cindex .#, lock file names
 
   When two users edit the same file at the same time, they are likely
 to interfere with each other.  Emacs tries to prevent this situation
@@ -720,8 +721,17 @@ modified.
 Emacs can then detect the first attempt to modify a buffer visiting a
 file that is locked by another Emacs job, and ask the user what to do.
 The file lock is really a file, a symbolic link with a special name,
-stored in the same directory as the file you are editing.  (On file
-systems that do not support symbolic links, a regular file is used.)
+stored in the same directory as the file you are editing.  The name is
+constructed by prepending @file{.#} to the filename of the buffer.
+The target of the symbolic link will be of the form
+@code{@var{user}@@@var{host}.@var{pid}:@var{boot}}, where @var{user}
+is replaced with the current username (from @code{user-login-name}),
+@var{host} with the name of the host where Emacs is running (from
+@code{system-name}), @var{pid} with Emacs's process id, and @var{boot}
+with the time since the last reboot.  @code{:@var{boot}} is omitted if
+the boot time is unavailable.  (On file systems that do not support
+symbolic links, a regular file is used instead, with contents of the
+form @code{@var{user}@@@var{host}.@var{pid}:@var{boot}}.)
 
   When you access files using NFS, there may be a small probability that
 you and another user will both lock the same file simultaneously.