[PATCH RFC 0/3] ext2fsprogs: Symlink support and doc fix

[PATCH RFC 0/3] ext2fsprogs: Symlink support and doc fix

[Darren Hart]

As we appear to have agreed that adding symlink support to debugfs via a new
ext2fs_symlink() function in libext2fs was something that needed doing, I
thought I'd use this as a trial run for my first contribution to the ext2fsprogs
package before I continue working on the larger project of completing initial
directory support for mke2fs.

While I modeled this patch after existing code, their were some inconcsistencies
in the code examples I used that I'd welcome input on. In particular:

o Should the ext2fs_link() happen right after ext2fs_new_inode()? Or should it
  happen closer to the end of the operation? do_write() and ext2fs_mkdir()
  handle this differently.

o Is it necessary to allocate the first block and assign it to the inode or the
  extents? ext2fs_mkdir() does this, do_write() does not. I opted for the
  simpler of the two and it passes my initial simple tests.

o Should I pass "mode" to ext2fs_new_inode() even though it is ignored?

o Would it make sense to try once to expand_dir rather than bailing out of
  ext2fs_mkdir() and ext2fs_symlink() if the directory is full?

o What would we like the initial uid,gid,mode,*time values to be for
  files/directories/links/etc. created with libext2fs?

Finally, I made an attempt to follow the coding style I observed in the code,
but if I missed something, please let me know.

Thanks,

Darren Hart
Intel Open Source Technology Center

[PATCH 1/3] lib/ext2fs: Correct interates typo in texinfo docs

[Darren Hart]

Just a typo fix.

Signed-off-by: Darren Hart <dvhart@infradead.org>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Andreas Dilger <adilger@dilger.ca>
---
 doc/libext2fs.texinfo | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/doc/libext2fs.texinfo b/doc/libext2fs.texinfo
index 9d8e7f1..8272d1d 100644
--- a/doc/libext2fs.texinfo
+++ b/doc/libext2fs.texinfo
@@ -767,7 +767,7 @@ to initialize directory entries for @file{.} and @file{..}, respectively.
 
 @deftypefun errcode_t ext2fs_dir_iterate (ext2_filsys @var{fs}, ext2_ino_t @var{dir}, int @var{flags}, char *@var{block_buf}, int (*@var{func})(struct ext2_dir_entry *@var{dirent}, int @var{offset}, int @var{blocksize}, char *@var{buf}, void *@var{private}), void *@var{private})
 
-This function interates over all of the directory entries in the
+This function iterates over all of the directory entries in the
 directory @var{dir}, calling the callback function @var{func} for each
 directory entry in the directory.  The @var{block_buf} parameter should
 either be NULL, or if the @code{ext2fs_dir_iterate} function is 
-- 
1.7.11.7

[PATCH 2/3] lib/ext2fs: Add ext2fs_symlink

[Darren Hart]

Creating symlinks is a complex affair when accounting for slowlinks.

Create a new function, ext2fs_symlink(), modeled after ext2fs_mkdir()
with input from debugfs's do_write() and copy_file(). Like
ext2fs_mkdir(), ext2fs_symlink() takes on the task of allocating a new
inode, setting up sane default values in the inode, accounting for the
inode stats, and copying the target path to either the inode (for
fastlinks) or to the blocks/extents (for slowlinks) using
ext2fs_file_write().

It does not attempt to expand the parent directory, instead returning
EXT2_ET_DIR_NO_SPACE and leaving it to the caller to expand just as
ext2fs_mkdir() does. Ideally, I think both of these functions should
make a single attempt to expand the directory.

Adds 1556 bytes to libext2fs.a (stripped).

Signed-off-by: Darren Hart <dvhart@infradead.org>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Andreas Dilger <adilger@dilger.ca>
---
 lib/ext2fs/Makefile.in    |   8 +++
 lib/ext2fs/ext2_err.et.in |   3 +
 lib/ext2fs/symlink.c      | 137 ++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 148 insertions(+)
 create mode 100644 lib/ext2fs/symlink.c

diff --git a/lib/ext2fs/Makefile.in b/lib/ext2fs/Makefile.in
index e05b438..5411826 100644
--- a/lib/ext2fs/Makefile.in
+++ b/lib/ext2fs/Makefile.in
@@ -80,6 +80,7 @@ OBJS= $(DEBUGFS_LIB_OBJS) $(RESIZE_LIB_OBJS) $(E2IMAGE_LIB_OBJS) \
 	res_gdt.o \
 	rw_bitmaps.o \
 	swapfs.o \
+	symlink.o \
 	tdb.o \
 	undo_io.o \
 	unix_io.o \
@@ -155,6 +156,7 @@ SRCS= ext2_err.c \
 	$(srcdir)/res_gdt.c \
 	$(srcdir)/rw_bitmaps.c \
 	$(srcdir)/swapfs.c \
+	$(srcdir)/symlink.c \
 	$(srcdir)/tdb.c \
 	$(srcdir)/test_io.c \
 	$(srcdir)/tst_badblocks.c \
@@ -881,6 +883,12 @@ swapfs.o: $(srcdir)/swapfs.c $(top_builddir)/lib/config.h \
  $(srcdir)/ext2_fs.h $(srcdir)/ext3_extents.h $(top_srcdir)/lib/et/com_err.h \
  $(srcdir)/ext2_io.h $(top_builddir)/lib/ext2fs/ext2_err.h \
  $(srcdir)/ext2_ext_attr.h $(srcdir)/bitops.h
+symlink.o: $(srcdir)/symlink.c $(top_builddir)/lib/config.h \
+ $(top_builddir)/lib/dirpaths.h $(srcdir)/ext2_fs.h \
+ $(top_builddir)/lib/ext2fs/ext2_types.h $(srcdir)/ext2fs.h \
+ $(srcdir)/ext2_fs.h $(srcdir)/ext3_extents.h $(top_srcdir)/lib/et/com_err.h \
+ $(srcdir)/ext2_io.h $(top_builddir)/lib/ext2fs/ext2_err.h \
+ $(srcdir)/ext2_ext_attr.h $(srcdir)/bitops.h
 tdb.o: $(srcdir)/tdb.c $(top_builddir)/lib/config.h \
  $(top_builddir)/lib/dirpaths.h $(srcdir)/tdb.h
 test_io.o: $(srcdir)/test_io.c $(top_builddir)/lib/config.h \
diff --git a/lib/ext2fs/ext2_err.et.in b/lib/ext2fs/ext2_err.et.in
index c99a167..e1313a8 100644
--- a/lib/ext2fs/ext2_err.et.in
+++ b/lib/ext2fs/ext2_err.et.in
@@ -248,6 +248,9 @@ ec	EXT2_ET_DB_NOT_FOUND,
 ec	EXT2_ET_DIR_EXISTS,
 	"Ext2 directory already exists"
 
+ec	EXT2_ET_FILE_EXISTS,
+	"Ext2 file already exists"
+
 ec	EXT2_ET_UNIMPLEMENTED,
 	"Unimplemented ext2 library function"
 
diff --git a/lib/ext2fs/symlink.c b/lib/ext2fs/symlink.c
new file mode 100644
index 0000000..5bfb9fc
--- /dev/null
+++ b/lib/ext2fs/symlink.c
@@ -0,0 +1,137 @@
+/*
+ * symlink.c --- make a symlink in the filesystem, based on mkdir.c
+ *
+ * Copyright (c) 2012, Intel Corporation.
+ * All Rights Reserved.
+ *
+ * %Begin-Header%
+ * This file may be redistributed under the terms of the GNU Library
+ * General Public License, version 2.
+ * %End-Header%
+ */
+
+#include "config.h"
+#include <stdio.h>
+#include <string.h>
+#if HAVE_UNISTD_H
+#include <unistd.h>
+#endif
+#include <fcntl.h>
+#include <time.h>
+#if HAVE_SYS_STAT_H
+#include <sys/stat.h>
+#endif
+#if HAVE_SYS_TYPES_H
+#include <sys/types.h>
+#endif
+
+#include "ext2_fs.h"
+#include "ext2fs.h"
+
+#ifndef EXT2_FT_SYMLINK
+#define EXT2_FT_SYMLINK		7
+#endif
+
+errcode_t ext2fs_symlink(ext2_filsys fs, ext2_ino_t parent, ext2_ino_t ino,
+                         const char *name, char *target)
+{
+	ext2_extent_handle_t	handle;
+	errcode_t		retval;
+	struct ext2_inode	inode;
+	ext2_ino_t		scratch_ino;
+	int			fastlink;
+	int			target_len;
+
+	EXT2_CHECK_MAGIC(fs, EXT2_ET_MAGIC_EXT2FS_FILSYS);
+
+	/*
+	 * Allocate an inode, if necessary
+	 */
+	if (!ino) {
+		retval = ext2fs_new_inode(fs, parent, LINUX_S_IFLNK | 0755,
+		                          0, &ino);
+		if (retval)
+			goto cleanup;
+	}
+
+	/*
+	 * Link the symlink into the filesystem hierarchy
+	 */
+	retval = ext2fs_lookup(fs, parent, name, strlen(name), 0,
+	                       &scratch_ino);
+	if (!retval) {
+		retval = EXT2_ET_FILE_EXISTS;
+		goto cleanup;
+	}
+	if (retval != EXT2_ET_FILE_NOT_FOUND)
+		goto cleanup;
+	retval = ext2fs_link(fs, parent, name, ino, EXT2_FT_SYMLINK);
+	if (retval)
+		goto cleanup;
+
+	ext2fs_inode_alloc_stats2(fs, ino, +1, 1);
+
+	/*
+	 * Create the inode structure....
+	 */
+	memset(&inode, 0, sizeof(struct ext2_inode));
+	inode.i_mode = LINUX_S_IFLNK | 0777;
+	inode.i_uid = inode.i_gid = 0;
+	/* FIXME: set the time fields */
+	inode.i_links_count = 1;
+
+	target_len = strlen(target);
+	fastlink = (target_len < sizeof(inode.i_block));
+	if (fastlink) {
+		/* Fast symlinks, target stored in inode */
+		inode.i_size = target_len;
+		strcpy((char *)&inode.i_block, target);
+	} else {
+		if (retval)
+			goto cleanup;
+
+		if (fs->super->s_feature_incompat & EXT3_FEATURE_INCOMPAT_EXTENTS)
+			inode.i_flags |= EXT4_EXTENTS_FL;
+
+		inode.i_size = (target_len % fs->blocksize) ?
+		               target_len + (fs->blocksize - target_len) : target_len;
+	}
+
+	/*
+	 * Write out the inode and inode data block.  The inode generation
+	 * number is assigned by write_new_inode, which means that the file
+	 * operations below should come after it.
+	 */
+	retval = ext2fs_write_new_inode(fs, ino, &inode);
+	if (retval)
+		goto cleanup;
+
+	/*
+	 * For slow links, the target path is written to the blocks/extents
+	 */
+	if (!fastlink) {
+		ext2_extent_handle_t handle;
+		ext2_file_t file;
+		int written = 0;
+		char *rem;
+
+		/* Write the target to file */
+		retval = ext2fs_file_open2(fs, ino, &inode,
+		                           EXT2_FILE_CREATE | EXT2_FILE_WRITE,
+		                           &file);
+		if (retval)
+			goto cleanup;
+
+		rem = target;
+		while (strlen(rem)) {
+			retval = ext2fs_file_write(file, (void *)rem, strlen(rem), &written);
+			rem += written;
+			if (retval)
+				break;
+		}
+		ext2fs_file_close(file);
+	}
+
+cleanup:
+	return retval;
+}
-- 
1.7.11.7

[PATCH 3/3] debugfs: Add symlink command

[Darren Hart]

Add support for symbolic links using a new symlink command.
Modeled after the do_mkdir() command.

Very long target paths fail as the command parsing appears to truncate the
input to somewhere around 256 bytes. Independent testing of the
ext2fs_symlink() command demonstrates it works with multi-block-length
pathes.

Signed-off-by: Darren Hart <dvhart@infradead.org>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Andreas Dilger <adilger@dilger.ca>
---
 debugfs/debug_cmds.ct |  3 +++
 debugfs/debugfs.8.in  |  3 +++
 debugfs/debugfs.c     | 43 +++++++++++++++++++++++++++++++++++++++++++
 debugfs/debugfs.h     |  1 +
 debugfs/dump.c        |  2 +-
 5 files changed, 51 insertions(+), 1 deletion(-)

diff --git a/debugfs/debug_cmds.ct b/debugfs/debug_cmds.ct
index a799dd7..338192f 100644
--- a/debugfs/debug_cmds.ct
+++ b/debugfs/debug_cmds.ct
@@ -160,6 +160,9 @@ request do_bmap, "Calculate the logical->physical block mapping for an inode",
 request do_punch, "Punch (or truncate) blocks from an inode by deallocating them",
 	punch, truncate;
 
+request do_symlink, "Create a symbolic link",
+	symlink;
+
 request do_imap, "Calculate the location of an inode",
 	imap;
 
diff --git a/debugfs/debugfs.8.in b/debugfs/debugfs.8.in
index bfcb1a8..c3b49f9 100644
--- a/debugfs/debugfs.8.in
+++ b/debugfs/debugfs.8.in
@@ -469,6 +469,9 @@ is, all of the blocks starting at
 .I start_blk
 through to the end of the file will be deallocated.
 .TP
+.I symlink filespec target
+Make a symbolic link.
+.TP
 .I pwd
 Print the current working directory.
 .TP
diff --git a/debugfs/debugfs.c b/debugfs/debugfs.c
index aec61ab..6c4c1b1 100644
--- a/debugfs/debugfs.c
+++ b/debugfs/debugfs.c
@@ -2204,6 +2204,49 @@ void do_punch(int argc, char *argv[])
 }
 #endif /* READ_ONLY */
 
+void do_symlink(int argc, char *argv[])
+{
+	char		*cp;
+	ext2_ino_t	parent;
+	char		*name, *target;
+	errcode_t	retval;
+
+	if (common_args_process(argc, argv, 3, 3, "symlink",
+				"<filename> <target>", CHECK_FS_RW))
+		return;
+
+	cp = strrchr(argv[1], '/');
+	if (cp) {
+		*cp = 0;
+		parent = string_to_inode(argv[1]);
+		if (!parent) {
+			com_err(argv[1], ENOENT, 0);
+			return;
+		}
+		name = cp+1;
+	} else {
+		parent = cwd;
+		name = argv[1];
+	}
+	target = argv[2];
+
+try_again:
+	retval = ext2fs_symlink(current_fs, parent, 0, name, target);
+	if (retval == EXT2_ET_DIR_NO_SPACE) {
+		retval = ext2fs_expand_dir(current_fs, parent);
+		if (retval) {
+			com_err(argv[0], retval, "while expanding directory");
+			return;
+		}
+		goto try_again;
+	}
+	if (retval) {
+		com_err("ext2fs_symlink", retval, 0);
+		return;
+	}
+
+}
+
 void do_dump_mmp(int argc EXT2FS_ATTR((unused)), char *argv[])
 {
 #if CONFIG_MMP
diff --git a/debugfs/debugfs.h b/debugfs/debugfs.h
index 994577c..434dbf0 100644
--- a/debugfs/debugfs.h
+++ b/debugfs/debugfs.h
@@ -133,6 +133,7 @@ extern void do_imap(int argc, char **argv);
 extern void do_set_current_time(int argc, char **argv);
 extern void do_supported_features(int argc, char **argv);
 extern void do_punch(int argc, char **argv);
+extern void do_symlink(int argc, char **argv);
 
 extern void do_dump_mmp(int argc, char **argv);
 extern void do_set_mmp_value(int argc, char **argv);
diff --git a/debugfs/dump.c b/debugfs/dump.c
index a15a0b7..2d830c9 100644
--- a/debugfs/dump.c
+++ b/debugfs/dump.c
@@ -285,7 +285,7 @@ static void rdump_inode(ext2_ino_t ino, struct ext2_inode *inode,
 
 		fix_perms("rdump", inode, -1, fullname);
 	}
-	/* else do nothing (don't dump device files, sockets, fifos, etc.) */
+	/* else do nothing (don't dump device files, sockets, fifos, symlinks, etc.) */
 
 errout:
 	free(fullname);
-- 
1.7.11.7

Re: [PATCH RFC 0/3] ext2fsprogs: Symlink support and doc fix

[Darren Hart]

Just a bump as a reminder so this series doesn't drop off the Inbox
queue :-)

Thanks,

Darren

On 12/05/2012 01:56 PM, Darren Hart wrote:
> As we appear to have agreed that adding symlink support to debugfs via a new
> ext2fs_symlink() function in libext2fs was something that needed doing, I
> thought I'd use this as a trial run for my first contribution to the ext2fsprogs
> package before I continue working on the larger project of completing initial
> directory support for mke2fs.
> 
> While I modeled this patch after existing code, their were some inconcsistencies
> in the code examples I used that I'd welcome input on. In particular:
> 
> o Should the ext2fs_link() happen right after ext2fs_new_inode()? Or should it
>   happen closer to the end of the operation? do_write() and ext2fs_mkdir()
>   handle this differently.
> 
> o Is it necessary to allocate the first block and assign it to the inode or the
>   extents? ext2fs_mkdir() does this, do_write() does not. I opted for the
>   simpler of the two and it passes my initial simple tests.
> 
> o Should I pass "mode" to ext2fs_new_inode() even though it is ignored?
> 
> o Would it make sense to try once to expand_dir rather than bailing out of
>   ext2fs_mkdir() and ext2fs_symlink() if the directory is full?
> 
> o What would we like the initial uid,gid,mode,*time values to be for
>   files/directories/links/etc. created with libext2fs?
> 
> Finally, I made an attempt to follow the coding style I observed in the code,
> but if I missed something, please let me know.
> 
> Thanks,
> 
> Darren Hart
> Intel Open Source Technology Center
> --
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> 

-- 
Darren Hart
Intel Open Source Technology Center
Yocto Project - Technical Lead - Linux Kernel