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* [glibc/azanella/posix_spawn-optimizations] Linux: Add internal direntries interface
@ 2019-07-30 21:30 Adhemerval Zanella
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From: Adhemerval Zanella @ 2019-07-30 21:30 UTC (permalink / raw)
To: glibc-cvs
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=0841f12653e9af21543805a4c3944f5e17da219a
commit 0841f12653e9af21543805a4c3944f5e17da219a
Author: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Date: Mon Jul 15 17:40:27 2019 -0300
Linux: Add internal direntries interface
Add new internal interfaces direntries_init, direntries_read, and
direntries_next meant to access directories entries similar to dirent
functions. Using these interfaces together with getdents64 has the
following benefits:
* The combination is async-signal-safe, since the buffer is allocated
externally to the call.
* There is no buffer bloat due to auto-sizing the DIR * buffer based on
preferred I/O sizes, as advertised by the file system.
* The combination does not suffer from the telldir problem (which
returns long on 32-bit architectures, which is incompatible with
struct dirent64 in the kernel). (Only seeking to the beginning is
supported.)
* Exposing the block read size means that the application knows when it
has to rewind after deleting enumerated files, to avoid skipping
entries or returning entries twice.
* sysdeps/unix/sysv/linux/Makefile (sysdep_routines): Add direntries.
* sysdeps/unix/sysv/linux/direntries.c: New file.
* sysdeps/unix/sysv/linux/direntries.h. Likewise.
Diff:
---
sysdeps/unix/sysv/linux/Makefile | 3 +-
sysdeps/unix/sysv/linux/direntries.c | 71 ++++++++++++++++++++++++++++++++++
sysdeps/unix/sysv/linux/direntries.h | 74 ++++++++++++++++++++++++++++++++++++
3 files changed, 147 insertions(+), 1 deletion(-)
diff --git a/sysdeps/unix/sysv/linux/Makefile b/sysdeps/unix/sysv/linux/Makefile
index 1ab6bcb..641c0c8 100644
--- a/sysdeps/unix/sysv/linux/Makefile
+++ b/sysdeps/unix/sysv/linux/Makefile
@@ -197,7 +197,8 @@ endif
inhibit-glue = yes
ifeq ($(subdir),dirent)
-sysdep_routines += getdirentries getdirentries64
+sysdep_routines += getdirentries getdirentries64 \
+ direntries
tests += tst-getdents64
tests-internal += tst-readdir64-compat
endif
diff --git a/sysdeps/unix/sysv/linux/direntries.c b/sysdeps/unix/sysv/linux/direntries.c
new file mode 100644
index 0000000..bf83a98
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/direntries.c
@@ -0,0 +1,71 @@
+/* Parsing directory streams. Linux version.
+ Copyright (C) 2019 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library 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
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <http://www.gnu.org/licenses/>. */
+
+#include <stdio.h>
+#include <dirent.h>
+
+#include <direntries.h>
+
+void
+__direntries_init (struct direntries *iterator, void *buffer, size_t length)
+{
+ /* Cheap security check if the caller accidentally passed an error
+ result from getdirentries to this function. */
+ if ((ssize_t) length < 0)
+ __fortify_fail ("invalid direntries_init call");
+
+ iterator->direntries_buffer_begin = buffer;
+ iterator->direntries_buffer_end = (char *) buffer + length;
+}
+
+ssize_t
+__direntries_read (int fd, struct direntries *iterator,
+ void *buffer, size_t length)
+{
+ ssize_t ret = __getdents64 (fd, buffer, length);
+ if (ret < 0)
+ return ret;
+ __direntries_init (iterator, buffer, ret);
+ return ret;
+}
+
+int
+__direntries_next (struct direntries *iterator, struct direntry *result)
+{
+ if (iterator->direntries_buffer_begin == iterator->direntries_buffer_end)
+ {
+ __set_errno (ENOENT);
+ return -1;
+ }
+
+ char *begin = iterator->direntries_buffer_begin;
+
+ /* The caller may have supplied an unaligned buffer. Make an
+ aligned copy of the entry, excluding its name. */
+ struct dirent64 entry;
+ memcpy (&entry, begin, offsetof (struct dirent64, d_name));
+
+ /* The name is not copied. It points into the existing buffer. */
+ result->d_name = begin + offsetof (struct dirent64, d_name);
+ result->d_ino = entry.d_ino;
+ result->d_type = entry.d_type;
+ result->d_flags = 0;
+
+ iterator->direntries_buffer_begin = begin + entry.d_reclen;
+ return 0;
+}
diff --git a/sysdeps/unix/sysv/linux/direntries.h b/sysdeps/unix/sysv/linux/direntries.h
new file mode 100644
index 0000000..4d4ca32
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/direntries.h
@@ -0,0 +1,74 @@
+/* Parsing directory streams. Linux version.
+ Copyright (C) 2019 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library 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
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <http://www.gnu.org/licenses/>. */
+
+#ifndef _SYS_DIRENTRIES_H
+#define _SYS_DIRENTRIES_H
+
+#include <features.h>
+#include <sys/types.h>
+
+/* One directory entry. See struct dirent in <dirent.h>. The main
+ difference is that d_name is a pointer here, and not an array, as
+ in struct dirent. */
+struct direntry
+{
+ /* Name of the directory entry. The string is part of the buffer
+ passed to direntries_init or direntries_read below. */
+ const char *d_name;
+
+ /* Inode number of this directory entry. */
+ __ino64_t d_ino;
+
+ /* Type of the entry. Can be DT_UNKNOWN if unknown. */
+ unsigned char d_type;
+
+ /* Currently always zero. */
+ unsigned char d_flags;
+};
+
+/* Initialized by direntries_init or direntires_read below and used by
+ direntry_next. */
+struct direntries
+{
+ void *direntries_buffer_begin;
+ void *direntries_buffer_end;
+};
+
+/* Initialize *ITERATOR based on BUFFER and LENGTH. BUFFER must have
+ been filled by getdents, and length must be a non-negative return
+ value from this function. Afterwards, individual entries can be
+ retrieved using direntries_next. */
+void __direntries_init (struct direntries *__iterator, void *__buffer,
+ size_t __length)
+ attribute_hidden __nonnull ((1, 2));
+
+/* Read directory entries from FD and write them to LENGTH bytes at
+ BUFFER and initialize *ITERATOR so that individual entries can be
+ retrieved using direntries_next. Returns -1 on error, 0 on end of
+ stream, and a positive value in case of more data. */
+__ssize_t __direntries_read (int __fd, struct direntries *__iterator,
+ void *__buffer, size_t __length) attribute_hidden
+ attribute_hidden __nonnull ((2, 3)) __wur;
+
+/* If there is a next entry, copy the next directory entry in ITERATOR
+ to *ENTRY, update *ITERATOR, and returns 0. If there is no next
+ entry, return -1 and set errno to ENOENT. */
+int __direntries_next (struct direntries *__iterator, struct direntry *__entry)
+ attribute_hidden __nonnull ((1, 2)) __wur;
+
+#endif /* _SYS_DIRENTRIES_H */
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