[RFC PATCH 1/2] Union Mount: glibc readdir support

bsn.0007
2008-04-29T13:39:29Z

Enhance readdir to support union mounted directories.

readdir now caches the dirents obtained from readdir(2)/getdents(2)
to support duplicate elimination and whiteout suppression for union
mounted directories.

Signed-off-by: Nagabhushan B S <bsn.0007@gmail.com>
---
sysdeps/unix/closedir.c | 14 +++++++++
sysdeps/unix/dirstream.h | 27 ++++++++++++++++++
sysdeps/unix/opendir.c | 4 ++
sysdeps/unix/readdir.c | 69 +++++++++++++++++++++++++++++++++++++++++++++--
4 files changed, 112 insertions(+), 2 deletions(-)

--- a/sysdeps/unix/closedir.c
+++ b/sysdeps/unix/closedir.c
@@ -32,6 +32,7 @@ int
__closedir (DIR *dirp)
{
int fd;
+ struct union_dir_cache *temp = NULL;

if (dirp == NULL)
{
@@ -49,6 +50,19 @@ __closedir (DIR *dirp)
__libc_lock_fini (dirp->lock);
#endif

+ if (dirp->head != NULL)
+ {
+ while (dirp->head->next != NULL)
+ {
+ temp = dirp->head->next;
+ free (dirp->head);
+ dirp->head = temp;
+ }
+ free (dirp->head);
+ dirp->head = NULL;
+ dirp->current = NULL;
+ }
+
free ((void *) dirp);

return close_not_cancel (fd);
--- a/sysdeps/unix/dirstream.h
+++ b/sysdeps/unix/dirstream.h
@@ -16,6 +16,20 @@
Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
02111-1307 USA. */

+#ifndef _UNION_DIR_CACHE
+#define _UNION_DIR_CACHE 1
+
+#include <limits.h>
+
+struct union_dir_cache
+{
+ char fname[NAME_MAX];
+ struct union_dir_cache *next;
+ struct union_dir_cache *prev;
+};
+
+#endif
+
#ifndef _DIRSTREAM_H
#define _DIRSTREAM_H 1

@@ -23,6 +37,14 @@

#include <bits/libc-lock.h>

+#define DIR_FIRST_DIRENT 1
+#define DIR_UNION_MOUNTED 2
+#define DIR_DUP_ELIM_START 4
+
+#define IS_FIRST_DIRENT(dirp) (dirp->union_dir_status & DIR_FIRST_DIRENT)
+#define IS_DIR_UNION_MOUNTED(dirp) (dirp->union_dir_status & DIR_UNION_MOUNTED)
+#define IS_DUP_ELIM_STARTED(dirp) (dirp->union_dir_status & DIR_DUP_ELIM_START)
+
/* Directory stream type.

The miscellaneous Unix `readdir' implementations read directory data
@@ -40,6 +62,11 @@ struct __dirstream

off_t filepos; /* Position of next entry to read. */

+ /* Cache of dirents to be used with union mounted directories */
+ struct union_dir_cache *head;
+ struct union_dir_cache *current;
+ unsigned char union_dir_status;
+
/* Directory block. */
char data[0] __attribute__ ((aligned (__alignof__ (void*))));
};
--- a/sysdeps/unix/opendir.c
+++ b/sysdeps/unix/opendir.c
@@ -202,6 +202,10 @@ __alloc_dir (int fd, bool close_fd, cons
dirp->size = 0;
dirp->offset = 0;
dirp->filepos = 0;
+ dirp->head = NULL;
+ dirp->current = NULL;
+ dirp->union_dir_status = 1;
+ dirp->union_dir_pos = 0;

return dirp;
}
--- a/sysdeps/unix/readdir.c
+++ b/sysdeps/unix/readdir.c
@@ -38,6 +38,9 @@
DIRENT_TYPE *
__READDIR (DIR *dirp)
{
+ int isdup;
+ struct union_dir_cache *temp = NULL;
+
DIRENT_TYPE *dp;
int saved_errno = errno;

@@ -108,8 +111,70 @@ __READDIR (DIR *dirp)
dirp->filepos += reclen;
#endif

- /* Skip deleted files. */
- } while (dp->d_ino == 0);
+ if (IS_FIRST_DIRENT(dirp))
+ {
+ if (dp->d_type == DT_WHT && !strcmp (dp->d_name, "."))
+ dirp->union_dir_status |= DIR_UNION_MOUNTED;
+ }
+
+ if (IS_DIR_UNION_MOUNTED(dirp) && !IS_FIRST_DIRENT(dirp))
+ {
+ /* Skip a file with 0 inode number, make sure that
+ it is not a whiteout type of file. We can get a "." whiteout
+ with inode number 0 at the beginning of each directory. */
+ if (dp->d_ino == 0 && dp->d_type != DT_WHT)
+ continue;
+
+ if (dp->d_type == DT_WHT && !strcmp (dp->d_name, "."))
+ dirp->union_dir_status |= DIR_DUP_ELIM_START;
+
+ isdup = 0;
+ if (IS_DUP_ELIM_STARTED(dirp))
+ {
+ /* Check if the dirent is already present in our cache */
+ temp = dirp->head;
+ while (temp)
+ {
+ if (!strcmp (temp->fname, dp->d_name))
+ {
+ isdup = 1;
+ break;
+ }
+ temp = temp->next;
+ }
+ }
+
+ if (isdup)
+ {
+ /* Found a duplicate, don't include it in dirent cache */
+ dp->d_ino = 0;
+ continue;
+ }
+
+ temp = (struct union_dir_cache *) malloc (sizeof (struct union_dir_cache));
+ temp->next = NULL;
+ temp->prev = NULL;
+
+
+ if (!dirp->head) /* Reading this dir first time. */
+ {
+ dirp->head = temp;
+ dirp->current = temp;
+ }
+ else
+ {
+ dirp->current->next = temp;
+ temp->prev = dirp->current;
+ dirp->current = dirp->current->next;
+ }
+
+ strcpy(dirp->current->fname, dp->d_name);
+
+ }
+ dirp->union_dir_status &= ~DIR_FIRST_DIRENT;
+
+ /* Skip deleted files. */
+ } while (dp->d_ino == 0 || dp->d_type == DT_WHT);

#ifndef NOT_IN_libc
__libc_lock_unlock (dirp->lock);