64-bit inodes (ino64) Status Update and Call for Testing

[Konstantin Belousov]

On Sun, May 21, 2017 at 02:14:56PM +0200, Jilles Tjoelker wrote:
> We have another type in this area which is too small in some situations:
> uint8_t for struct dirent.d_namlen. For filesystems that store filenames
> as upto 255 UTF-16 code units, the name to be stored in d_name may be
> upto 765 bytes long in UTF-8. This was reported in PR 204643. The code
> currently handles this by returning the short (8.3) name, but this name
> may not be present or usable, leaving the file inaccessible.
> 
> Actually allowing longer names seems too complicated to add to the ino64
> change, but changing d_namlen to uint16_t (using d_pad0 space) and
> skipping entries with d_namlen > 255 in libc may be helpful.
> 
> Note that applications using the deprecated readdir_r() will not be able
> to read such long names, since the API does not allow specifying that a
> larger buffer has been provided. (This could be avoided by making struct
> dirent.d_name 766 bytes long instead of 256.)
> 
> Unfortunately, the existence of readdir_r() also prevents changing
> struct dirent.d_name to the more correct flexible array.

Yes, changing the size of d_name at this stage of the project is out of
question. My reading of your proposal is that we should extend the size
of d_namlen to uint16_t, am I right ? Should we go to 32bit directly
then, perhaps ?

I did not committed the change below, nor did I tested or even build it.

diff --git a/lib/libc/gen/readdir-compat11.c b/lib/libc/gen/readdir-compat11.c
index 1c52f563c75..18d85adaa63 100644
--- a/lib/libc/gen/readdir-compat11.c
+++ b/lib/libc/gen/readdir-compat11.c
@@ -41,6 +41,7 @@ __FBSDID("$FreeBSD$");
 #define	_WANT_FREEBSD11_DIRENT
 #include <dirent.h>
 #include <errno.h>
+#include <stdbool.h>
 #include <stddef.h>
 #include <stdlib.h>
 #include <string.h>
@@ -53,10 +54,12 @@ __FBSDID("$FreeBSD$");
 
 #include "gen-compat.h"
 
-static void
+static bool
 freebsd11_cvtdirent(struct freebsd11_dirent *dstdp, struct dirent *srcdp)
 {
 
+	if (srcdp->d_namelen >= sizeof(dstdp->d_name))
+		return (false);
 	dstdp->d_type = srcdp->d_type;
 	dstdp->d_namlen = srcdp->d_namlen;
 	dstdp->d_fileno = srcdp->d_fileno;		/* truncate */
@@ -65,6 +68,7 @@ freebsd11_cvtdirent(struct freebsd11_dirent *dstdp, struct dirent *srcdp)
 	bzero(dstdp->d_name + dstdp->d_namlen,
 	    dstdp->d_reclen - offsetof(struct freebsd11_dirent, d_name) -
 	    dstdp->d_namlen);
+	return (true);
 }
 
 struct freebsd11_dirent *
@@ -80,8 +84,10 @@ freebsd11_readdir(DIR *dirp)
 		if (dirp->dd_compat_de == NULL)
 			dirp->dd_compat_de = malloc(sizeof(struct
 			    freebsd11_dirent));
-		freebsd11_cvtdirent(dirp->dd_compat_de, dp);
-		dstdp = dirp->dd_compat_de;
+		if (freebsd11_cvtdirent(dirp->dd_compat_de, dp))
+			dstdp = dirp->dd_compat_de;
+		else
+			dstdp = NULL;
 	} else
 		dstdp = NULL;
 	if (__isthreaded)
@@ -101,8 +107,10 @@ freebsd11_readdir_r(DIR *dirp, struct freebsd11_dirent *entry,
 	if (error != 0)
 		return (error);
 	if (xresult != NULL) {
-		freebsd11_cvtdirent(entry, &xentry);
-		*result = entry;
+		if (freebsd11_cvtdirent(entry, &xentry))
+			*result = entry;
+		else
+			*result = NULL;
 	} else
 		*result = NULL;
 	return (0);
diff --git a/sys/kern/vfs_syscalls.c b/sys/kern/vfs_syscalls.c
index 784af836aee..27b2635030d 100644
--- a/sys/kern/vfs_syscalls.c
+++ b/sys/kern/vfs_syscalls.c
@@ -3733,7 +3733,8 @@ freebsd11_kern_getdirentries(struct thread *td, int fd, char *ubuf, u_int count,
 		if (dp->d_reclen == 0)
 			break;
 		MPASS(dp->d_reclen >= _GENERIC_DIRLEN(0));
-		/* dp->d_namlen <= sizeof(dstdp.d_name) - 1 always */
+		if (dp->d_namlen >= sizeof(dstdp.d_name))
+			continue;
 		dstdp.d_type = dp->d_type;
 		dstdp.d_namlen = dp->d_namlen;
 		dstdp.d_fileno = dp->d_fileno;		/* truncate */
diff --git a/sys/sys/dirent.h b/sys/sys/dirent.h
index 341855d0530..691c4e8f90f 100644
--- a/sys/sys/dirent.h
+++ b/sys/sys/dirent.h
@@ -67,8 +67,9 @@ struct dirent {
 	off_t      d_off;		/* directory offset of entry */
 	__uint16_t d_reclen;		/* length of this record */
 	__uint8_t  d_type;		/* file type, see below */
-	__uint8_t  d_namlen;		/* length of string in d_name */
-	__uint32_t d_pad0;
+	__uint8_t  d_pad0
+	__uint16_t d_namlen;		/* length of string in d_name */
+	__uint16_t d_pad1;
 #if __BSD_VISIBLE
 #define	MAXNAMLEN	255
 	char	d_name[MAXNAMLEN + 1];	/* name must be no longer than this */