On Sunday 03 April 2016 16:30:48 Matteo Cafasso wrote:

The internal_filesystem_walk command walks through the FS structure of a disk partition and returns all the files or directories which could be found.

The command is able to retrieve information regarding deleted or unaccessible files as well where other commands such as stat or find would fail.

The gathered list of tsk_dirent structs is serialised into XDR format and written to a file by the appliance.

Not that it is a big issue, but you can wrap commit messages at the 72 columns.

Signed-off-by: Matteo Cafasso <noxdafox@gmail.com> --- daemon/Makefile.am | 4 +- daemon/tsk.c | 225 +++++++++++++++++++++++++++++++++++++++++++++++++++ generator/actions.ml | 25 ++++++ src/MAX_PROC_NR | 2 +- 4 files changed, 254 insertions(+), 2 deletions(-) create mode 100644 daemon/tsk.c

diff --git a/daemon/Makefile.am b/daemon/Makefile.am index beb7962..03bf71f 100644 --- a/daemon/Makefile.am +++ b/daemon/Makefile.am @@ -179,6 +179,7 @@ guestfsd_SOURCES = \ sync.c \ syslinux.c \ tar.c \ + tsk.c \ truncate.c \ umask.c \ upload.c \ @@ -209,7 +210,8 @@ guestfsd_LDADD = \ $(LIB_CLOCK_GETTIME) \ $(LIBINTL) \ $(SERVENT_LIB) \ - $(PCRE_LIBS) + $(PCRE_LIBS) \ + $(TSK_LIBS)

guestfsd_CPPFLAGS = \ -I$(top_srcdir)/gnulib/lib \ diff --git a/daemon/tsk.c b/daemon/tsk.c new file mode 100644 index 0000000..ac44106 --- /dev/null +++ b/daemon/tsk.c @@ -0,0 +1,225 @@ +/* libguestfs - the guestfsd daemon + * Copyright (C) 2016 Red Hat Inc. + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 2 of the License, or + * (at your option) any later version. + * + * This program 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 General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, write to the Free Software + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. + */ + +#include <config.h> + +#include <stdio.h> +#include <stdlib.h> +#include <inttypes.h> +#include <string.h> +#include <unistd.h> +#include <rpc/xdr.h> +#include <rpc/types.h> + +#include "guestfs_protocol.h" +#include "daemon.h" +#include "actions.h" +#include "optgroups.h" + +#ifdef HAVE_LIBTSK + +#include <tsk/libtsk.h> + +/* File types map similar to dirent. */ +#define TSK_FILE_TYPE_NUM 10 +char TSK_FILE_TYPE[TSK_FILE_TYPE_NUM] = { + 'u', 'f', 'c', 'd', 'b', 'r', 'l', 's', 'h', 'w' +};

I see the libtsk already uses TSK_* and tsk_* prefixes for its own stuff, so I'd avoid using the same prefixes for local variables. Also, make the string as static const, since it does not need to be modified at all (and thus can then be placed into .rodata).

+ +static int open_filesystem (const char *device, + TSK_IMG_INFO **img, TSK_FS_INFO **fs); +static TSK_WALK_RET_ENUM fswalk_callback (TSK_FS_FILE *fsfile, + const char *path, void *data);

Single line for forward declarations.

+static char file_type (TSK_FS_FILE *fsfile); +static int send_dirent_info (guestfs_int_tsk_dirent *dirent); +static void reply_with_tsk_error (const char *funcname); + +int +do_internal_filesystem_walk (const mountable_t *mountable) +{ + int ret = -1; + TSK_FS_INFO *fs = NULL; + TSK_IMG_INFO *img = NULL; /* Used internally by tsk_fs_dir_walk */ + int flags = TSK_FS_DIR_WALK_FLAG_ALLOC | TSK_FS_DIR_WALK_FLAG_UNALLOC | + TSK_FS_DIR_WALK_FLAG_RECURSE | TSK_FS_DIR_WALK_FLAG_NOORPHAN; + + ret = open_filesystem (mountable->device, &img, &fs); + if (ret < 0) + return ret; + + reply (NULL, NULL); /* Reply message. */ + + ret = tsk_fs_dir_walk (fs, fs->root_inum, flags, fswalk_callback, NULL); + if (ret == 0) + ret = send_file_end (0); /* File transfer end. */ + else + send_file_end (1); /* Cancel file transfer. */ + + fs->close (fs); + img->close (img); + + return ret; +} + +/* Inspect the device and initialises the img and fs structures. + * Return 0 on success, -1 on error. + */ +static int +open_filesystem (const char *device, TSK_IMG_INFO **img, TSK_FS_INFO **fs) +{ + const char *images[] = { device }; + + *img = tsk_img_open (1, images, TSK_IMG_TYPE_DETECT , 0); + if (*img == NULL) { + reply_with_tsk_error ("tsk_image_open"); + return -1; + } + + *fs = tsk_fs_open_img (*img, 0, TSK_FS_TYPE_DETECT); + if (*fs == NULL) { + reply_with_tsk_error ("tsk_fs_open_img"); + (*img)->close (*img); + return -1; + } + + return 0; +} + +/* Filesystem walk callback, it gets called on every FS node. + * Parse the node, encode it into an XDR structure and send it to the appliance. + * Return TSK_WALK_CONT on success, TSK_WALK_ERROR on error. + */ +static TSK_WALK_RET_ENUM +fswalk_callback (TSK_FS_FILE *fsfile, const char *path, void *data) +{ + int ret = 0; + CLEANUP_FREE char *fname = NULL; + struct guestfs_int_tsk_dirent dirent; + + /* Ignore ./ and ../ */ + ret = TSK_FS_ISDOT (fsfile->name->name); + if (ret != 0) + return TSK_WALK_CONT; + + /* Build the full relative path of the entry */ + ret = asprintf_nowarn (&fname, "%Q%Q", path, fsfile->name->name);

Why the quoting? We don't quote results in similar APIs (e.g. readdir).

+ if (ret < 0) { + fprintf (stderr, "asprintf: %m"); + return TSK_WALK_ERROR; + } + + dirent.tsk_inode = fsfile->name->meta_addr; + dirent.tsk_type = file_type (fsfile); + dirent.tsk_size = (fsfile->meta != NULL) ? fsfile->meta->size : 0;

If 'meta' is null, then I guess the size should be -1 to indicate it was not available; otherwise, there is no difference between an empty file, and a file whose metadata could not be read.

+ dirent.tsk_name = fname; + dirent.tsk_allocated = !(fsfile->name->flags & TSK_FS_NAME_FLAG_UNALLOC); + + ret = send_dirent_info (&dirent); + ret = (ret == 0) ? TSK_WALK_CONT : TSK_WALK_ERROR; + + return ret; +} + +/* Inspect fsfile to identify its type. */ +static char +file_type(TSK_FS_FILE *fsfile) +{ + if (fsfile->name->type < TSK_FILE_TYPE_NUM) + return TSK_FILE_TYPE[fsfile->name->type]; + else if (fsfile->meta != NULL && fsfile->meta->type < TSK_FILE_TYPE_NUM) + return TSK_FILE_TYPE[fsfile->meta->type]; + else + return 'u'; +}

I think it would be better to have a switch case on the file type: the current solution will silently break if a future (incompatible) version of libtsk changes the order/values of the elements in TSK_FS_NAME_TYPE_ENUM. Also, new values are simply not detected at all, whereas with a switch case at least they would give us compiler warnings. Also, IMHO code like: switch (type) { case TSK_FS_NAME_TYPE_UNDEF: return 'u'; ... would be much more readable.

+/* Serialise dirent into XDR stream and send it to the appliance. + * Return 0 on success, -1 on error. + */ +static int +send_dirent_info (guestfs_int_tsk_dirent *dirent) +{ + XDR xdr; + size_t len = 0; + CLEANUP_FREE char *buf; + + buf = malloc (GUESTFS_MAX_CHUNK_SIZE); + if (buf == NULL) { + fprintf (stderr, "malloc: %m"); + return -1; + } + + /* Serialise tsk_dirent struct. */ + xdrmem_create (&xdr, buf, GUESTFS_MAX_CHUNK_SIZE, XDR_ENCODE); + + if (!xdr_uint64_t (&xdr, &dirent->tsk_inode)) + return -1; + if (!xdr_char (&xdr, &dirent->tsk_type)) + return -1; + if (!xdr_int64_t (&xdr, &dirent->tsk_size)) + return -1; + + /* Serialise filename. */ + len = strlen (dirent->tsk_name) + 1; + if (!xdr_u_long (&xdr, &len)) + return -1; + if (!xdr_string (&xdr, &dirent->tsk_name, len)) + return -1; + + if (!xdr_uint32_t (&xdr, &dirent->tsk_allocated)) + return -1; + + /* Resize buffer to actual length. */ + len = xdr_getpos (&xdr); + xdr_destroy (&xdr); + buf = realloc (buf, len); + if (buf == NULL) { + fprintf (stderr, "realloc: %m"); + return -1; + }

I think this manual code is not needed, and you can use the XDR serializing functions generated in daemon/guestfs_protocol.{c,h}.

+ + /* Send serialised tsk_dirent out. */ + return send_file_write (buf, len); +} + +/* Parse TSK error and send it to the appliance. */ +static void +reply_with_tsk_error (const char *funcname) +{ + int ret = 0; + const char *buf = NULL; + + ret = tsk_error_get_errno (); + if (ret != 0) { + buf = tsk_error_get (); + reply_with_error ("TSK function %s error: %s", funcname, buf); + } + else + reply_with_error ("TSK function %s: unknown error", funcname); +}

s/TSK function//

+ +int +optgroup_libtsk_available (void) +{ + return 1; +} + +#else /* !HAVE_LIBTSK */ + +OPTGROUP_LIBTSK_NOT_AVAILABLE + +#endif /* !HAVE_LIBTSK */ diff --git a/generator/actions.ml b/generator/actions.ml index e5cb939..449ffa0 100644 --- a/generator/actions.ml +++ b/generator/actions.ml @@ -12958,6 +12958,31 @@ and save it as F<filename> on the local machine.

This allows to download deleted or inaccessible files." };

+ { defaults with + name = "internal_filesystem_walk"; added = (1, 33, 17); + style = RErr, [Mountable "device"; FileOut "filename"], []; + proc_nr = Some 465; + visibility = VInternal; + optional = Some "libtsk"; + shortdesc = "walk through the filesystem content"; + longdesc = "Walk through the internal structures of a disk partition +(eg. F</dev/sda1>) in order to return a list of all the files +and directories stored within. + +It is not necessary to mount the disk partition to run this command. + +All entries in the filesystem are returned, excluding C<.> and +C<..>. This function can list deleted or unaccessible files. +The entries are I<not> sorted. + +If the entry is not allocated (ex: it has been deleted), +its inode, type or size might not be recovered correctly. +In such case, the inode and the size will be 0 while the type +will be unidentified 'u'. + +This call returns basic file type information about each +file." };

No need to copy&paste the same description used for the public filesystem_walk -- a one-liner telling it is an internal function for filesystem_walk is enough. Internal functions will not be documented anyway, so it is not worth adding "proper" documentation text for them. Thanks, -- Pino Toscano

Hi, some of the comments for patch #3 apply also for this one, namely: - wrapping of commit message - indentation of forward declarations - usage of XDR deserialization from guestfs_protocol.h - On Sunday 03 April 2016 16:30:49 Matteo Cafasso wrote:

The filesystem_walk command is the appliance's counterpart of the daemon's internal_filesystem_walk command.

It writes the daemon's command output on a temporary file and parses it, deserialising the XDR formatted tsk_dirent structs.

It returns to the caller the list of tsk_dirent structs generated by the internal_filesystem_walk command.

Signed-off-by: Matteo Cafasso <noxdafox@gmail.com> --- generator/actions.ml | 69 ++++++++++++++++++++++ src/Makefile.am | 1 + src/tsk.c | 162 +++++++++++++++++++++++++++++++++++++++++++++++++++ 3 files changed, 232 insertions(+) create mode 100644 src/tsk.c

diff --git a/generator/actions.ml b/generator/actions.ml index 449ffa0..9457c3f 100644 --- a/generator/actions.ml +++ b/generator/actions.ml @@ -3546,6 +3546,75 @@ The environment variable C<XDG_RUNTIME_DIR> controls the default value: If C<XDG_RUNTIME_DIR> is set, then that is the default. Else F</tmp> is the default." };

+ { defaults with + name = "filesystem_walk"; added = (1, 33, 17); + style = RStructList ("dirents", "tsk_dirent"), [Mountable "device";], []; + optional = Some "libtsk"; + progress = true; cancellable = true; + shortdesc = "walk through the filesystem content"; + longdesc = "\ +Walk through the internal structures of a disk partition +(eg. F</dev/sda1>) in order to return a list of all the files +and directories stored within. + +It is not necessary to mount the disk partition to run this command. + +All entries in the filesystem are returned, excluding C<.> and +C<..>. This function can list deleted or unaccessible files. +The entries are I<not> sorted. + +If the entry is not allocated (ex: it has been deleted), +its inode, type or size might not be recovered correctly. +In such case, the inode and the size will be 0 while the type +will be unidentified 'u'.

As said for patch #3, unknown sizes should be -1 and not 0.

+This call returns as well basic file type information about each +file. The C<tsk_type> field will contain one of the following characters: + +=over 4 + +=item 'b' + +Block special + +=item 'c' + +Char special + +=item 'd' + +Directory + +=item 'f' + +FIFO (named pipe) + +=item 'l' + +Symbolic link + +=item 'r' + +Regular file + +=item 's' + +Socket + +=item 'h' + +Shadow inode (Solaris) + +=item 'w' + +Whiteout inode (BSD) + +=item 'u' + +Unknown file type + +=back" }; + ]

(* daemon_functions are any functions which cause some action diff --git a/src/Makefile.am b/src/Makefile.am index 3b4cd10..9f8af4c 100644 --- a/src/Makefile.am +++ b/src/Makefile.am @@ -130,6 +130,7 @@ libguestfs_la_SOURCES = \ structs-copy.c \ structs-free.c \ tmpdirs.c \ + tsk.c \ whole-file.c \ libguestfs.syms

diff --git a/src/tsk.c b/src/tsk.c new file mode 100644 index 0000000..d77bc0a --- /dev/null +++ b/src/tsk.c @@ -0,0 +1,162 @@ +/* libguestfs + * Copyright (C) 2016 Red Hat Inc. + * + * This 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 of the License, or (at your option) any later version. + * + * This 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 this library; if not, write to the Free Software + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA + */ + +#include <config.h> + +#include <stdio.h> +#include <stdlib.h> +#include <fcntl.h> +#include <unistd.h> +#include <sys/types.h> +#include <sys/stat.h> +#include <string.h> +#include <rpc/xdr.h> +#include <rpc/types.h> + +#include "full-read.h" + +#include "guestfs.h" +#include "guestfs_protocol.h" +#include "guestfs-internal.h" +#include "guestfs-internal-all.h" +#include "guestfs-internal-actions.h" + +static struct guestfs_tsk_dirent_list *parse_filesystem_walk +(guestfs_h *g, char *buf, size_t bufsize); +int deserialise_dirent_list (guestfs_h *g, char *buf, size_t bufsize, + struct guestfs_tsk_dirent_list **dirents); +static int deserialise_dirent (guestfs_h *g, XDR *xdrs, + struct guestfs_tsk_dirent *dirent); + +struct guestfs_tsk_dirent_list * +guestfs_impl_filesystem_walk (guestfs_h *g, const char *mountable) +{ + int ret = 0; + size_t size = 0; + CLEANUP_FREE char *buf = NULL; + CLEANUP_UNLINK_FREE char *tmpfile = NULL; + + ret = guestfs_int_lazy_make_tmpdir (g); + if (ret < 0) + return NULL; + + tmpfile = safe_asprintf (g, "%s/filesystem_walk%d", g->tmpdir, ++g->unique); + + ret = guestfs_internal_filesystem_walk (g, mountable, tmpfile); + if (ret < 0) + return NULL; + + ret = guestfs_int_read_whole_file (g, tmpfile, &buf, &size); + if (ret < 0) + return NULL; + + return parse_filesystem_walk (g, buf, size); /* caller frees */ +} + +/* Parse buf content and return dirents list. + * Return a list of tsk_dirent on success, NULL on error. + */ +static struct guestfs_tsk_dirent_list * +parse_filesystem_walk (guestfs_h *g, char *buf, size_t bufsize) +{ + int ret = 0; + struct guestfs_tsk_dirent_list *dirents = NULL; + + /* Initialise results array. */ + dirents = safe_malloc (g, sizeof (struct guestfs_tsk_dirent_list)); + dirents->len = 8; + dirents->val = safe_malloc (g, dirents->len * + sizeof (struct guestfs_tsk_dirent));

sizeof (*dirents->val) (and below too) can make the code slightly shorter (just an hint).

+ + /* Deserialise buffer into dirent list. */ + ret = deserialise_dirent_list (g, buf, bufsize, &dirents); + if (ret < 0) { + guestfs_free_tsk_dirent_list (dirents); + return NULL; + } + + /* Resize the array to correct number of entries. */ + dirents->len = ret; + dirents->val = safe_realloc (g, dirents->val, + dirents->len * + sizeof (struct guestfs_tsk_dirent));

You don't need to shrink the array with values -- users knows already they don't have to access it past 'len' values.

+ + return dirents; +} + +/* Deserialise buf content and populate the dirent list. + * Return the number of deserialised dirents, -1 on error. + */ +int +deserialise_dirent_list (guestfs_h *g, char *buf, size_t bufsize, + struct guestfs_tsk_dirent_list **dirents)

Since you don't change the location of 'dirents', you don't need to pass a pointer to it to change its values. Thanks, -- Pino Toscano

On Monday 04 April 2016 15:00:26 NoxDaFox wrote:

2016-04-04 13:09 GMT+03:00 Pino Toscano <ptoscano@redhat.com>:

...

Hi,

some of the comments for patch #3 apply also for this one, namely: - wrapping of commit message - indentation of forward declarations - usage of XDR deserialization from guestfs_protocol.h -

On Sunday 03 April 2016 16:30:49 Matteo Cafasso wrote:

...

The filesystem_walk command is the appliance's counterpart of the daemon's internal_filesystem_walk command.

It writes the daemon's command output on a temporary file and parses it, deserialising the XDR formatted tsk_dirent structs.

It returns to the caller the list of tsk_dirent structs generated by the internal_filesystem_walk command.

Signed-off-by: Matteo Cafasso <noxdafox@gmail.com> --- generator/actions.ml | 69 ++++++++++++++++++++++ src/Makefile.am | 1 + src/tsk.c | 162 +++++++++++++++++++++++++++++++++++++++++++++++++++ 3 files changed, 232 insertions(+) create mode 100644 src/tsk.c

diff --git a/generator/actions.ml b/generator/actions.ml index 449ffa0..9457c3f 100644 --- a/generator/actions.ml +++ b/generator/actions.ml @@ -3546,6 +3546,75 @@ The environment variable C<XDG_RUNTIME_DIR> controls the default value: If C<XDG_RUNTIME_DIR> is set, then that is the default. Else F</tmp> is the default." };

+ { defaults with + name = "filesystem_walk"; added = (1, 33, 17); + style = RStructList ("dirents", "tsk_dirent"), [Mountable "device";], []; + optional = Some "libtsk"; + progress = true; cancellable = true; + shortdesc = "walk through the filesystem content"; + longdesc = "\ +Walk through the internal structures of a disk partition +(eg. F</dev/sda1>) in order to return a list of all the files +and directories stored within. + +It is not necessary to mount the disk partition to run this command. + +All entries in the filesystem are returned, excluding C<.> and +C<..>. This function can list deleted or unaccessible files. +The entries are I<not> sorted. + +If the entry is not allocated (ex: it has been deleted), +its inode, type or size might not be recovered correctly. +In such case, the inode and the size will be 0 while the type +will be unidentified 'u'.

As said for patch #3, unknown sizes should be -1 and not 0.

...

+This call returns as well basic file type information about each +file. The C<tsk_type> field will contain one of the following characters: + +=over 4 + +=item 'b' + +Block special + +=item 'c' + +Char special + +=item 'd' + +Directory + +=item 'f' + +FIFO (named pipe) + +=item 'l' + +Symbolic link + +=item 'r' + +Regular file + +=item 's' + +Socket + +=item 'h' + +Shadow inode (Solaris) + +=item 'w' + +Whiteout inode (BSD) + +=item 'u' + +Unknown file type + +=back" }; + ]

(* daemon_functions are any functions which cause some action diff --git a/src/Makefile.am b/src/Makefile.am index 3b4cd10..9f8af4c 100644 --- a/src/Makefile.am +++ b/src/Makefile.am @@ -130,6 +130,7 @@ libguestfs_la_SOURCES = \ structs-copy.c \ structs-free.c \ tmpdirs.c \ + tsk.c \ whole-file.c \ libguestfs.syms

diff --git a/src/tsk.c b/src/tsk.c new file mode 100644 index 0000000..d77bc0a --- /dev/null +++ b/src/tsk.c @@ -0,0 +1,162 @@ +/* libguestfs + * Copyright (C) 2016 Red Hat Inc. + * + * This 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 of the License, or (at your option) any later version. + * + * This 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 this library; if not, write to the Free Software + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA + */ + +#include <config.h> + +#include <stdio.h> +#include <stdlib.h> +#include <fcntl.h> +#include <unistd.h> +#include <sys/types.h> +#include <sys/stat.h> +#include <string.h> +#include <rpc/xdr.h> +#include <rpc/types.h> + +#include "full-read.h" + +#include "guestfs.h" +#include "guestfs_protocol.h" +#include "guestfs-internal.h" +#include "guestfs-internal-all.h" +#include "guestfs-internal-actions.h" + +static struct guestfs_tsk_dirent_list *parse_filesystem_walk +(guestfs_h *g, char *buf, size_t bufsize); +int deserialise_dirent_list (guestfs_h *g, char *buf, size_t bufsize, + struct guestfs_tsk_dirent_list **dirents); +static int deserialise_dirent (guestfs_h *g, XDR *xdrs, + struct guestfs_tsk_dirent *dirent); + +struct guestfs_tsk_dirent_list * +guestfs_impl_filesystem_walk (guestfs_h *g, const char *mountable) +{ + int ret = 0; + size_t size = 0; + CLEANUP_FREE char *buf = NULL; + CLEANUP_UNLINK_FREE char *tmpfile = NULL; + + ret = guestfs_int_lazy_make_tmpdir (g); + if (ret < 0) + return NULL; + + tmpfile = safe_asprintf (g, "%s/filesystem_walk%d", g->tmpdir, ++g->unique); + + ret = guestfs_internal_filesystem_walk (g, mountable, tmpfile); + if (ret < 0) + return NULL; + + ret = guestfs_int_read_whole_file (g, tmpfile, &buf, &size); + if (ret < 0) + return NULL; + + return parse_filesystem_walk (g, buf, size); /* caller frees */ +} + +/* Parse buf content and return dirents list. + * Return a list of tsk_dirent on success, NULL on error. + */ +static struct guestfs_tsk_dirent_list * +parse_filesystem_walk (guestfs_h *g, char *buf, size_t bufsize) +{ + int ret = 0; + struct guestfs_tsk_dirent_list *dirents = NULL; + + /* Initialise results array. */ + dirents = safe_malloc (g, sizeof (struct guestfs_tsk_dirent_list)); + dirents->len = 8; + dirents->val = safe_malloc (g, dirents->len * + sizeof (struct guestfs_tsk_dirent));

sizeof (*dirents->val) (and below too) can make the code slightly shorter (just an hint).

...

+ + /* Deserialise buffer into dirent list. */ + ret = deserialise_dirent_list (g, buf, bufsize, &dirents); + if (ret < 0) { + guestfs_free_tsk_dirent_list (dirents); + return NULL; + } + + /* Resize the array to correct number of entries. */ + dirents->len = ret; + dirents->val = safe_realloc (g, dirents->val, + dirents->len * + sizeof (struct guestfs_tsk_dirent));

You don't need to shrink the array with values -- users knows already they don't have to access it past 'len' values.

If I then run the command in guestfish I get plenty of empty structs.

Right, that's why setting the right size is the important bit. I was referring to the realloc which shrinks (or not) the memory of the array. -- Pino Toscano