From 8654f9d7d6d7c3ee97232a34a40250dcbc57af8e Mon Sep 17 00:00:00 2001 From: Paul Eggert Date: Thu, 31 Jan 2013 22:30:51 -0800 Subject: 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 . (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 , . (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 , . (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 --- lib/fdopendir.c | 204 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 204 insertions(+) create mode 100644 lib/fdopendir.c (limited to 'lib/fdopendir.c') diff --git a/lib/fdopendir.c b/lib/fdopendir.c new file mode 100644 index 00000000000..63e06b92ae8 --- /dev/null +++ b/lib/fdopendir.c @@ -0,0 +1,204 @@ +/* provide a replacement fdopendir function + Copyright (C) 2004-2013 Free Software Foundation, Inc. + + This program is free software: you can redistribute it and/or modify + it under the terms of the GNU General Public License as published by + the Free Software Foundation; either version 3 of the License, or + (at your option) any later version. + + This program is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + GNU General Public License for more details. + + You should have received a copy of the GNU General Public License + along with this program. If not, see . */ + +/* written by Jim Meyering */ + +#include + +#include + +#include +#include + +#if !HAVE_FDOPENDIR + +# include "openat.h" +# include "openat-priv.h" +# include "save-cwd.h" + +# if GNULIB_DIRENT_SAFER +# include "dirent--.h" +# endif + +# ifndef REPLACE_FCHDIR +# define REPLACE_FCHDIR 0 +# endif + +static DIR *fdopendir_with_dup (int, int, struct saved_cwd const *); +static DIR *fd_clone_opendir (int, struct saved_cwd const *); + +/* Replacement for POSIX fdopendir. + + First, try to simulate it via opendir ("/proc/self/fd/..."). Failing + that, simulate it by using fchdir metadata, or by doing + save_cwd/fchdir/opendir(".")/restore_cwd. + If either the save_cwd or the restore_cwd fails (relatively unlikely), + then give a diagnostic and exit nonzero. + + If successful, the resulting stream is based on FD in + implementations where streams are based on file descriptors and in + applications where no other thread or signal handler allocates or + frees file descriptors. In other cases, consult dirfd on the result + to find out whether FD is still being used. + + Otherwise, this function works just like POSIX fdopendir. + + W A R N I N G: + + Unlike other fd-related functions, this one places constraints on FD. + If this function returns successfully, FD is under control of the + dirent.h system, and the caller should not close or modify the state of + FD other than by the dirent.h functions. */ +DIR * +fdopendir (int fd) +{ + DIR *dir = fdopendir_with_dup (fd, -1, NULL); + + if (! REPLACE_FCHDIR && ! dir) + { + int saved_errno = errno; + if (EXPECTED_ERRNO (saved_errno)) + { + struct saved_cwd cwd; + if (save_cwd (&cwd) != 0) + openat_save_fail (errno); + dir = fdopendir_with_dup (fd, -1, &cwd); + saved_errno = errno; + free_cwd (&cwd); + errno = saved_errno; + } + } + + return dir; +} + +/* Like fdopendir, except that if OLDER_DUPFD is not -1, it is known + to be a dup of FD which is less than FD - 1 and which will be + closed by the caller and not otherwise used by the caller. This + function makes sure that FD is closed and all file descriptors less + than FD are open, and then calls fd_clone_opendir on a dup of FD. + That way, barring race conditions, fd_clone_opendir returns a + stream whose file descriptor is FD. + + If REPLACE_CHDIR or CWD is null, use opendir ("/proc/self/fd/...", + falling back on fchdir metadata. Otherwise, CWD is a saved version + of the working directory; use fchdir/opendir(".")/restore_cwd(CWD). */ +static DIR * +fdopendir_with_dup (int fd, int older_dupfd, struct saved_cwd const *cwd) +{ + int dupfd = dup (fd); + if (dupfd < 0 && errno == EMFILE) + dupfd = older_dupfd; + if (dupfd < 0) + return NULL; + else + { + DIR *dir; + int saved_errno; + if (dupfd < fd - 1 && dupfd != older_dupfd) + { + dir = fdopendir_with_dup (fd, dupfd, cwd); + saved_errno = errno; + } + else + { + close (fd); + dir = fd_clone_opendir (dupfd, cwd); + saved_errno = errno; + if (! dir) + { + int fd1 = dup (dupfd); + if (fd1 != fd) + openat_save_fail (fd1 < 0 ? errno : EBADF); + } + } + + if (dupfd != older_dupfd) + close (dupfd); + errno = saved_errno; + return dir; + } +} + +/* Like fdopendir, except the result controls a clone of FD. It is + the caller's responsibility both to close FD and (if the result is + not null) to closedir the result. */ +static DIR * +fd_clone_opendir (int fd, struct saved_cwd const *cwd) +{ + if (REPLACE_FCHDIR || ! cwd) + { + DIR *dir = NULL; + int saved_errno = EOPNOTSUPP; + char buf[OPENAT_BUFFER_SIZE]; + char *proc_file = openat_proc_name (buf, fd, "."); + if (proc_file) + { + dir = opendir (proc_file); + saved_errno = errno; + if (proc_file != buf) + free (proc_file); + } +# if REPLACE_FCHDIR + if (! dir && EXPECTED_ERRNO (saved_errno)) + { + char const *name = _gl_directory_name (fd); + return (name ? opendir (name) : NULL); + } +# endif + errno = saved_errno; + return dir; + } + else + { + if (fchdir (fd) != 0) + return NULL; + else + { + DIR *dir = opendir ("."); + int saved_errno = errno; + if (restore_cwd (cwd) != 0) + openat_restore_fail (errno); + errno = saved_errno; + return dir; + } + } +} + +#else /* HAVE_FDOPENDIR */ + +# include +# include + +# undef fdopendir + +/* Like fdopendir, but work around GNU/Hurd bug by validating FD. */ + +DIR * +rpl_fdopendir (int fd) +{ + struct stat st; + if (fstat (fd, &st)) + return NULL; + if (!S_ISDIR (st.st_mode)) + { + errno = ENOTDIR; + return NULL; + } + return fdopendir (fd); +} + +#endif /* HAVE_FDOPENDIR */ -- cgit v1.2.3