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author | Paul Eggert <eggert@cs.ucla.edu> | 2013-01-31 22:30:51 -0800 |
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committer | Paul Eggert <eggert@cs.ucla.edu> | 2013-01-31 22:30:51 -0800 |
commit | 8654f9d7d6d7c3ee97232a34a40250dcbc57af8e (patch) | |
tree | ff488081b57dabdfe7e85c11a34e8ac522b5bdb4 /lib/openat-proc.c | |
parent | 44b12dd6994a6214b9d6f73539b441080611369b (diff) | |
download | emacs-8654f9d7d6d7c3ee97232a34a40250dcbc57af8e.tar.gz |
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
Diffstat (limited to 'lib/openat-proc.c')
-rw-r--r-- | lib/openat-proc.c | 110 |
1 files changed, 110 insertions, 0 deletions
diff --git a/lib/openat-proc.c b/lib/openat-proc.c new file mode 100644 index 00000000000..d7a68e26d0b --- /dev/null +++ b/lib/openat-proc.c @@ -0,0 +1,110 @@ +/* Create /proc/self/fd-related names for subfiles of open directories. + + Copyright (C) 2006, 2009-2013 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 <http://www.gnu.org/licenses/>. */ + +/* Written by Paul Eggert. */ + +#include <config.h> + +#include "openat-priv.h" + +#include <sys/types.h> +#include <sys/stat.h> +#include <fcntl.h> + +#include <stdio.h> +#include <stdlib.h> +#include <string.h> +#include <unistd.h> + +#include "intprops.h" + +/* The results of open() in this file are not used with fchdir, + and we do not leak fds to any single-threaded code that could use stdio, + therefore save some unnecessary work in fchdir.c. + FIXME - if the kernel ever adds support for multi-thread safety for + avoiding standard fds, then we should use open_safer. */ +#undef open +#undef close + +#define PROC_SELF_FD_FORMAT "/proc/self/fd/%d/%s" + +#define PROC_SELF_FD_NAME_SIZE_BOUND(len) \ + (sizeof PROC_SELF_FD_FORMAT - sizeof "%d%s" \ + + INT_STRLEN_BOUND (int) + (len) + 1) + + +/* Set BUF to the expansion of PROC_SELF_FD_FORMAT, using FD and FILE + respectively for %d and %s. If successful, return BUF if the + result fits in BUF, dynamically allocated memory otherwise. But + return NULL if /proc is not reliable, either because the operating + system support is lacking or because memory is low. */ +char * +openat_proc_name (char buf[OPENAT_BUFFER_SIZE], int fd, char const *file) +{ + static int proc_status = 0; + + /* Make sure the caller gets ENOENT when appropriate. */ + if (!*file) + { + buf[0] = '\0'; + return buf; + } + + if (! proc_status) + { + /* Set PROC_STATUS to a positive value if /proc/self/fd is + reliable, and a negative value otherwise. Solaris 10 + /proc/self/fd mishandles "..", and any file name might expand + to ".." after symbolic link expansion, so avoid /proc/self/fd + if it mishandles "..". Solaris 10 has openat, but this + problem is exhibited on code that built on Solaris 8 and + running on Solaris 10. */ + + int proc_self_fd = open ("/proc/self/fd", + O_SEARCH | O_DIRECTORY | O_NOCTTY | O_NONBLOCK); + if (proc_self_fd < 0) + proc_status = -1; + else + { + /* Detect whether /proc/self/fd/%i/../fd exists, where %i is the + number of a file descriptor open on /proc/self/fd. On Linux, + that name resolves to /proc/self/fd, which was opened above. + However, on Solaris, it may resolve to /proc/self/fd/fd, which + cannot exist, since all names in /proc/self/fd are numeric. */ + char dotdot_buf[PROC_SELF_FD_NAME_SIZE_BOUND (sizeof "../fd" - 1)]; + sprintf (dotdot_buf, PROC_SELF_FD_FORMAT, proc_self_fd, "../fd"); + proc_status = access (dotdot_buf, F_OK) ? -1 : 1; + close (proc_self_fd); + } + } + + if (proc_status < 0) + return NULL; + else + { + size_t bufsize = PROC_SELF_FD_NAME_SIZE_BOUND (strlen (file)); + char *result = buf; + if (OPENAT_BUFFER_SIZE < bufsize) + { + result = malloc (bufsize); + if (! result) + return NULL; + } + sprintf (result, PROC_SELF_FD_FORMAT, fd, file); + return result; + } +} |