• Paul Eggert's avatar
    FILE's lock is now always .#FILE and may be a regular file. · 70743157
    Paul Eggert authored
    * etc/NEWS: Document this.
    * nt/inc/unistd.h (O_NOFOLLOW): New macro.
    * src/filelock.c: Include <c-ctype.h>.
    (MAX_LFINFO): New top-level constant.
    (lock_info_type): Remove members pid, boot_time.  Add members at,
    dot, colon.  Change user member to be the entire buffer, not a
    pointer.  This allows us to handle the case where a foreign
    pid or boot time exceeds the local range.  All uses changed.
    (LINKS_MIGHT_NOT_WORK): New constant.
    (FREE_LOCK_INFO): Remove, as the pieces no longer need freeing.
    (defined_WINDOWSNT): Remove.
    (MAKE_LOCK_NAME, file_in_lock_file_name):
    Always use .#FILE (not .#-FILE) for the file lock,
    even if it is a regular file.
    (rename_lock_file): New function.
    (create_lock_file): Use it.
    (create_lock_file, read_lock_data):
    Prefer a symbolic link for the lock file, falling back on a
    regular file if symlinks don't work.  Do not try to create
    symlinks on MS-Windows, due to security hassles.  Stick with
    POSIXish functions (open, read, write, close, fchmod, readlink, symlink,
    link, rename, unlink, mkstemp) when creating locks, as a GNUish
    host may be using a Windowsish file system, and cannot use
    MS-Windows-only system calls.  Fall back on mktemp if mkstemp
    doesn't work.  Don't fail merely because of a symlink-contents
    length limit in the current file system; fall back on regular
    files.  Increase the symlink contents length limit to 8 KiB, this
    should be big enough for any real use and doesn't crunch the
    stack.
    (create_lock_file, lock_file_1, read_lock_data):
    Simplify allocation of lock file buffers now that they fit in 8 KiB.
    (lock_file_1): Return error number, not bool.  All callers changed.
    (ELOOP): New macro, if not already defined.
    (read_lock_data): Return size of lock file contents, not Lisp object.
    All callers changed.  Handle a race condition if some other process
    replaces a regular-file lock with a symlink lock or vice versa,
    while we're trying to read the lock.
    (current_lock_owner): Parse contents more carefully, to help avoid
    confusing a regular-file lock with some other application's use
    of the file.  Check for lock file contents being too long, or
    not parsing correctly.
    (current_lock_owner, lock_file):
    Allow foreign pid and boot times that exceed the local range.
    (current_lock_owner, lock_if_free, lock_file):
    Simplify allocation of lock file contents.
    * src/w32.c (sys_rename_replace): New function, containing most of
    the contents of the old sys_rename.
    (sys_rename): Use it.
    (fchmod): New dummy function.
    * src/w32.h (sys_rename_replace, fchmod): New decls.
    
    Fixes: debbugs:13807
    70743157
NEWS 108 KB