Use fdopendir, fstatat and readlinkat, for efficiency.
On my host, this speeds up directory-files-and-attributes by a factor of 3, when applied to Emacs's src directory. These functions are standardized by POSIX and are common these days; fall back on a (slower) gnulib implementation if the host is too old to supply them. * .bzrignore: Add lib/dirent.h. * lib/Makefile.am (libgnu_a_SOURCES): Add openat-die.c, save-cwd.c. * lib/careadlinkat.c, lib/careadlinkat.h: Merge from gnulib, incorporating: 2013-01-29 careadlinkat: do not provide careadlinkatcwd. * lib/gnulib.mk, m4/gnulib-comp.m4: Regenerate. * lib/dirent.in.h, lib/fdopendir.c, lib/fstatat.c, lib/openat-priv.h: * lib/openat-proc.c, lib/openat.h, m4/dirent_h.m4, m4/fdopendir.m4: * m4/fstatat.m4: New files, from gnulib. * lib/openat-die.c, lib/save-cwd.c, lib/save-cwd.h: New files. These last three are specific to Emacs and are not copied from gnulib. They are simpler than the gnulib versions and are tuned for Emacs. * admin/merge-gnulib (GNULIB_MODULES): Add fdopendir, fstatat, readlinkat. (GNULIB_TOOL_FLAGS): Do not avoid at-internal, openat-h. Avoid dup, open, opendir. * nt/inc/sys/stat.h (fstatat): * nt/inc/unistd.h (readlinkat): New decls. * src/conf_post.h (GNULIB_SUPPORT_ONLY_AT_FDCWD): Remove. * src/dired.c: Include <fcntl.h>. (open_directory): New function, which uses open and fdopendir rather than opendir. DOS_NT platforms still use opendir, though. (directory_files_internal, file_name_completion): Use it. (file_attributes): New function, with most of the old Ffile_attributes. (directory_files_internal, Ffile_attributes): Use it. (file_attributes, file_name_completion_stat): First arg is now fd, not dir name. All uses changed. Use fstatat rather than lstat + stat. (file_attributes): Use emacs_readlinkat rather than Ffile_symlink_p. * src/fileio.c: Include <allocator.h>, <careadlinkat.h>. (emacs_readlinkat): New function, with much of the old Ffile_symlink_p, but with an fd argument for speed. It uses readlinkat rather than careadlinkatcwd, so that it need not assume the working directory. (Ffile_symlink_p): Use it. * src/filelock.c (current_lock_owner): Use emacs_readlinkat rather than emacs_readlink. * src/lisp.h (emacs_readlinkat): New decl. (READLINK_BUFSIZE, emacs_readlink): Remove. * src/sysdep.c: Do not include <allocator.h>, <careadlinkat.h>. (emacs_norealloc_allocator, emacs_readlink): Remove. This stuff is moved to fileio.c. * src/w32.c (fstatat, readlinkat): New functions. (careadlinkat): Don't check that fd == AT_FDCWD. (careadlinkatcwd): Remove; no longer needed. Fixes: debbugs:13539
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