281 lines
10 KiB
Diff
281 lines
10 KiB
Diff
diff --git a/manual/conf.texi b/manual/conf.texi
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index 7eb8b36..c720063 100644
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--- manual/conf.texi
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+++ manual/conf.texi
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@@ -1149,6 +1149,9 @@ typed ahead as input. @xref{I/O Queues}.
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@deftypevr Macro int NAME_MAX
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The uniform system limit (if any) for the length of a file name component, not
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including the terminating null character.
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+
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+@strong{Portability Note:} On some systems, @theglibc{} defines
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+@code{NAME_MAX}, but does not actually enforce this limit.
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@end deftypevr
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@comment limits.h
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@@ -1157,6 +1160,9 @@ including the terminating null character.
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The uniform system limit (if any) for the length of an entire file name (that
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is, the argument given to system calls such as @code{open}), including the
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terminating null character.
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+
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+@strong{Portability Note:} @Theglibc{} does not enforce this limit
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+even if @code{PATH_MAX} is defined.
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@end deftypevr
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@cindex limits, pipe buffer size
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@@ -1476,6 +1482,9 @@ Inquire about the value of @code{POSIX_REC_MIN_XFER_SIZE}.
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Inquire about the value of @code{POSIX_REC_XFER_ALIGN}.
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@end table
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+@strong{Portability Note:} On some systems, @theglibc{} does not
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+enforce @code{_PC_NAME_MAX} or @code{_PC_PATH_MAX} limits.
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+
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@node Utility Limits
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@section Utility Program Capacity Limits
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diff --git a/manual/filesys.texi b/manual/filesys.texi
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index 1df9cf2..814c210 100644
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--- manual/filesys.texi
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+++ manual/filesys.texi
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@@ -444,9 +444,9 @@ symbols are declared in the header file @file{dirent.h}.
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@comment POSIX.1
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@deftypefun {struct dirent *} readdir (DIR *@var{dirstream})
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This function reads the next entry from the directory. It normally
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-returns a pointer to a structure containing information about the file.
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-This structure is statically allocated and can be rewritten by a
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-subsequent call.
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+returns a pointer to a structure containing information about the
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+file. This structure is associated with the @var{dirstream} handle
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+and can be rewritten by a subsequent call.
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@strong{Portability Note:} On some systems @code{readdir} may not
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return entries for @file{.} and @file{..}, even though these are always
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@@ -461,19 +461,61 @@ conditions are defined for this function:
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The @var{dirstream} argument is not valid.
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@end table
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-@code{readdir} is not thread safe. Multiple threads using
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-@code{readdir} on the same @var{dirstream} may overwrite the return
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-value. Use @code{readdir_r} when this is critical.
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+To distinguish between an end-of-directory condition or an error, you
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+must set @code{errno} to zero before calling @code{readdir}. To avoid
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+entering an infinite loop, you should stop reading from the directory
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+after the first error.
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+
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+In POSIX.1-2008, @code{readdir} is not thread-safe. In @theglibc{}
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+implementation, it is safe to call @code{readdir} concurrently on
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+different @var{dirstream}s, but multiple threads accessing the same
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+@var{dirstream} result in undefined behavior. @code{readdir_r} is a
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+fully thread-safe alternative, but suffers from poor portability (see
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+below). It is recommended that you use @code{readdir}, with external
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+locking if multiple threads access the same @var{dirstream}.
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@end deftypefun
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@comment dirent.h
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@comment GNU
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@deftypefun int readdir_r (DIR *@var{dirstream}, struct dirent *@var{entry}, struct dirent **@var{result})
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-This function is the reentrant version of @code{readdir}. Like
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-@code{readdir} it returns the next entry from the directory. But to
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-prevent conflicts between simultaneously running threads the result is
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-not stored in statically allocated memory. Instead the argument
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-@var{entry} points to a place to store the result.
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+This function is a version of @code{readdir} which performs internal
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+locking. Like @code{readdir} it returns the next entry from the
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+directory. To prevent conflicts between simultaneously running
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+threads the result is stored inside the @var{entry} object.
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+
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+@strong{Portability Note:} It is recommended to use @code{readdir}
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+instead of @code{readdir_r} for the following reasons:
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+
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+@itemize @bullet
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+@item
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+On systems which do not define @code{NAME_MAX}, it may not be possible
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+to use @code{readdir_r} safely because the caller does not specify the
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+length of the buffer for the directory entry.
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+
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+@item
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+On some systems, @code{readdir_r} cannot read directory entries with
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+very long names. If such a name is encountered, @theglibc{}
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+implementation of @code{readdir_r} returns with an error code of
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+@code{ENAMETOOLONG} after the final directory entry has been read. On
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+other systems, @code{readdir_r} may return successfully, but the
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+@code{d_name} member may not be NUL-terminated or may be truncated.
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+
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+@item
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+POSIX-1.2008 does not guarantee that @code{readdir} is thread-safe,
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+even when access to the same @var{dirstream} is serialized. But in
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+current implementations (including @theglibc{}), it is safe to call
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+@code{readdir} concurrently on different @var{dirstream}s, so there is
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+no need to use @code{readdir_r} in most multi-threaded programs. In
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+the rare case that multiple threads need to read from the same
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+@var{dirstream}, it is still better to use @code{readdir} and external
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+synchronization.
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+
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+@item
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+It is expected that future versions of POSIX will obsolete
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+@code{readdir_r} and mandate the level of thread safety for
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+@code{readdir} which is provided by @theglibc{} and other
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+implementations today.
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+@end itemize
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Normally @code{readdir_r} returns zero and sets @code{*@var{result}}
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to @var{entry}. If there are no more entries in the directory or an
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@@ -481,15 +523,6 @@ error is detected, @code{readdir_r} sets @code{*@var{result}} to a
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null pointer and returns a nonzero error code, also stored in
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@code{errno}, as described for @code{readdir}.
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-@strong{Portability Note:} On some systems @code{readdir_r} may not
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-return a NUL terminated string for the file name, even when there is no
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-@code{d_reclen} field in @code{struct dirent} and the file
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-name is the maximum allowed size. Modern systems all have the
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-@code{d_reclen} field, and on old systems multi-threading is not
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-critical. In any case there is no such problem with the @code{readdir}
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-function, so that even on systems without the @code{d_reclen} member one
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-could use multiple threads by using external locking.
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-
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It is also important to look at the definition of the @code{struct
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dirent} type. Simply passing a pointer to an object of this type for
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the second parameter of @code{readdir_r} might not be enough. Some
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diff --git a/sysdeps/posix/dirstream.h b/sysdeps/posix/dirstream.h
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index a7a074d..8e8570d 100644
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--- sysdeps/posix/dirstream.h
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+++ sysdeps/posix/dirstream.h
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@@ -39,6 +39,8 @@ struct __dirstream
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off_t filepos; /* Position of next entry to read. */
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+ int errcode; /* Delayed error code. */
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+
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/* Directory block. */
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char data[0] __attribute__ ((aligned (__alignof__ (void*))));
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};
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diff --git a/sysdeps/posix/opendir.c b/sysdeps/posix/opendir.c
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index ddfc3a7..fc05b0f 100644
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--- sysdeps/posix/opendir.c
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+++ sysdeps/posix/opendir.c
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@@ -231,6 +231,7 @@ __alloc_dir (int fd, bool close_fd, int flags, const struct stat64 *statp)
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dirp->size = 0;
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dirp->offset = 0;
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dirp->filepos = 0;
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+ dirp->errcode = 0;
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return dirp;
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}
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diff --git a/sysdeps/posix/readdir_r.c b/sysdeps/posix/readdir_r.c
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index b5a8e2e..8ed5c3f 100644
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--- sysdeps/posix/readdir_r.c
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+++ sysdeps/posix/readdir_r.c
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@@ -40,6 +40,7 @@ __READDIR_R (DIR *dirp, DIRENT_TYPE *entry, DIRENT_TYPE **result)
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DIRENT_TYPE *dp;
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size_t reclen;
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const int saved_errno = errno;
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+ int ret;
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__libc_lock_lock (dirp->lock);
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@@ -70,10 +71,10 @@ __READDIR_R (DIR *dirp, DIRENT_TYPE *entry, DIRENT_TYPE **result)
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bytes = 0;
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__set_errno (saved_errno);
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}
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+ if (bytes < 0)
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+ dirp->errcode = errno;
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dp = NULL;
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- /* Reclen != 0 signals that an error occurred. */
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- reclen = bytes != 0;
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break;
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}
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dirp->size = (size_t) bytes;
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@@ -106,29 +107,46 @@ __READDIR_R (DIR *dirp, DIRENT_TYPE *entry, DIRENT_TYPE **result)
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dirp->filepos += reclen;
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#endif
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- /* Skip deleted files. */
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+#ifdef NAME_MAX
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+ if (reclen > offsetof (DIRENT_TYPE, d_name) + NAME_MAX + 1)
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+ {
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+ /* The record is very long. It could still fit into the
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+ caller-supplied buffer if we can skip padding at the
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+ end. */
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+ size_t namelen = _D_EXACT_NAMLEN (dp);
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+ if (namelen <= NAME_MAX)
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+ reclen = offsetof (DIRENT_TYPE, d_name) + namelen + 1;
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+ else
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+ {
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+ /* The name is too long. Ignore this file. */
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+ dirp->errcode = ENAMETOOLONG;
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+ dp->d_ino = 0;
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+ continue;
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+ }
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+ }
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+#endif
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+
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+ /* Skip deleted and ignored files. */
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}
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while (dp->d_ino == 0);
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if (dp != NULL)
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{
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-#ifdef GETDENTS_64BIT_ALIGNED
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- /* The d_reclen value might include padding which is not part of
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- the DIRENT_TYPE data structure. */
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- reclen = MIN (reclen,
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- offsetof (DIRENT_TYPE, d_name) + sizeof (dp->d_name));
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-#endif
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*result = memcpy (entry, dp, reclen);
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-#ifdef GETDENTS_64BIT_ALIGNED
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+#ifdef _DIRENT_HAVE_D_RECLEN
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entry->d_reclen = reclen;
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#endif
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+ ret = 0;
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}
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else
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- *result = NULL;
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+ {
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+ *result = NULL;
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+ ret = dirp->errcode;
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+ }
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__libc_lock_unlock (dirp->lock);
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- return dp != NULL ? 0 : reclen ? errno : 0;
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+ return ret;
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}
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#ifdef __READDIR_R_ALIAS
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diff --git a/sysdeps/posix/rewinddir.c b/sysdeps/posix/rewinddir.c
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index 2935a8e..d4991ad 100644
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--- sysdeps/posix/rewinddir.c
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+++ sysdeps/posix/rewinddir.c
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@@ -33,6 +33,7 @@ rewinddir (dirp)
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dirp->filepos = 0;
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dirp->offset = 0;
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dirp->size = 0;
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+ dirp->errcode = 0;
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#ifndef NOT_IN_libc
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__libc_lock_unlock (dirp->lock);
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#endif
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diff --git a/sysdeps/unix/sysv/linux/i386/readdir64_r.c b/sysdeps/unix/sysv/linux/i386/readdir64_r.c
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index 8ebbcfd..a7d114e 100644
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--- sysdeps/unix/sysv/linux/i386/readdir64_r.c
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+++ sysdeps/unix/sysv/linux/i386/readdir64_r.c
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@@ -18,7 +18,6 @@
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#define __READDIR_R __readdir64_r
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#define __GETDENTS __getdents64
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#define DIRENT_TYPE struct dirent64
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-#define GETDENTS_64BIT_ALIGNED 1
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#include <sysdeps/posix/readdir_r.c>
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diff --git a/sysdeps/unix/sysv/linux/wordsize-64/readdir_r.c b/sysdeps/unix/sysv/linux/wordsize-64/readdir_r.c
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index 5ed8e95..290f2c8 100644
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--- sysdeps/unix/sysv/linux/wordsize-64/readdir_r.c
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+++ sysdeps/unix/sysv/linux/wordsize-64/readdir_r.c
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@@ -1,5 +1,4 @@
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#define readdir64_r __no_readdir64_r_decl
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-#define GETDENTS_64BIT_ALIGNED 1
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#include <sysdeps/posix/readdir_r.c>
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#undef readdir64_r
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weak_alias (__readdir_r, readdir64_r)
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--
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1.8.3.4
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