Laszlo Ersek
2022-May-01 07:04 UTC
[Libguestfs] [libguestfs PATCH 0/2] lift protocol limit on guestfs_readdir()
Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1674392
Remove the GUESTFS_MESSAGE_MAX protocol limit from the last remaining
"high-profile" API, guestfs_readdir().
A fast reproducer is in
<https://bugzilla.redhat.com/show_bug.cgi?id=1674392#c27>.
Thanks
Laszlo
Laszlo Ersek (2):
guestfs_readdir(): rewrite with FileOut transfer, to lift protocol
limit
guestfs_readdir(): minimize the number of send_file_write() calls
TODO | 8 -
daemon/readdir.c | 156 ++++++++++++--------
generator/actions_core.ml | 127 ++++++++--------
generator/proc_nr.ml | 2 +-
lib/Makefile.am | 1 +
lib/readdir.c | 131 ++++++++++++++++
6 files changed, 291 insertions(+), 134 deletions(-)
create mode 100644 lib/readdir.c
base-commit: 0956e8e0c5b70e79a01f43046ac7be2b9a171ed8
--
2.19.1.3.g30247aa5d201
Laszlo Ersek
2022-May-01 07:04 UTC
[Libguestfs] [libguestfs PATCH 1/2] guestfs_readdir(): rewrite with FileOut transfer, to lift protocol limit
Currently the guestfs_readdir() API can not list long directories, due to
it sending back the whole directory listing in a single guestfs protocol
response, which is limited to GUESTFS_MESSAGE_MAX (approx. 4MB) in size.
Introduce the "internal_readdir" action, for transferring the
directory
listing from the daemon to the library through a FileOut parameter.
Rewrite guestfs_readdir() on top of this new internal function:
- The new "internal_readdir" action is a daemon action. Repurpose the
"readdir" proc_nr (138) for "internal_readdir". Assume the
new action
will first be released in libguestfs-1.48.2.
- Turn "readdir" from a daemon action into a non-daemon one. Call the
daemon action guestfs_internal_readdir() manually, receive the FileOut
parameter into a temp file, then deserialize the dirents array from the
temp file.
This patch sneakily fixes an independent bug, too. In the pre-patch
do_readdir() function [daemon/readdir.c], when readdir() returns NULL, we
don't distinguish "end of directory stream" from "readdir()
failed". This
rewrite fixes this problem -- I didn't see much value separating out the
fix for the original do_readdir().
Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1674392
Signed-off-by: Laszlo Ersek <lersek at redhat.com>
---
lib/Makefile.am | 1 +
generator/actions_core.ml | 127 ++++++++++---------
generator/proc_nr.ml | 2 +-
daemon/readdir.c | 132 ++++++++++----------
lib/readdir.c | 131 +++++++++++++++++++
TODO | 8 --
6 files changed, 266 insertions(+), 135 deletions(-)
diff --git a/lib/Makefile.am b/lib/Makefile.am
index 144c45588bfd..212bcb94aa12 100644
--- a/lib/Makefile.am
+++ b/lib/Makefile.am
@@ -105,6 +105,7 @@ libguestfs_la_SOURCES = \
private-data.c \
proto.c \
qemu.c \
+ readdir.c \
rescue.c \
stringsbuf.c \
structs-compare.c \
diff --git a/generator/actions_core.ml b/generator/actions_core.ml
index 23a2eabef87b..e70c77f44fae 100644
--- a/generator/actions_core.ml
+++ b/generator/actions_core.ml
@@ -141,6 +141,66 @@ only useful for printing debug and internal error messages.
For more information on states, see L<guestfs(3)>." };
+ { defaults with
+ name = "readdir"; added = (1, 0, 55);
+ style = RStructList ("entries", "dirent"), [String
(Pathname, "dir")], [];
+ progress = true; cancellable = true;
+ shortdesc = "read directories entries";
+ longdesc = "\
+This returns the list of directory entries in directory C<dir>.
+
+All entries in the directory are returned, including C<.> and
+C<..>. The entries are I<not> sorted, but returned in the same
+order as the underlying filesystem.
+
+Also this call returns basic file type information about each
+file. The C<ftyp> 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 'u'
+
+Unknown file type
+
+=item '?'
+
+The L<readdir(3)> call returned a C<d_type> field with an
+unexpected value
+
+=back
+
+This function is primarily intended for use by programs. To
+get a simple list of names, use C<guestfs_ls>. To get a printable
+directory for human consumption, use C<guestfs_ll>." };
+
{ defaults with
name = "version"; added = (1, 0, 58);
style = RStruct ("version", "version"), [], [];
@@ -3918,66 +3978,6 @@ L<umask(2)>, C<guestfs_mknod>,
C<guestfs_mkdir>.
This call returns the previous umask." };
- { defaults with
- name = "readdir"; added = (1, 0, 55);
- style = RStructList ("entries", "dirent"), [String
(Pathname, "dir")], [];
- protocol_limit_warning = true;
- shortdesc = "read directories entries";
- longdesc = "\
-This returns the list of directory entries in directory C<dir>.
-
-All entries in the directory are returned, including C<.> and
-C<..>. The entries are I<not> sorted, but returned in the same
-order as the underlying filesystem.
-
-Also this call returns basic file type information about each
-file. The C<ftyp> 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 'u'
-
-Unknown file type
-
-=item '?'
-
-The L<readdir(3)> call returned a C<d_type> field with an
-unexpected value
-
-=back
-
-This function is primarily intended for use by programs. To
-get a simple list of names, use C<guestfs_ls>. To get a printable
-directory for human consumption, use C<guestfs_ll>." };
-
{ defaults with
name = "getxattrs"; added = (1, 0, 59);
style = RStructList ("xattrs", "xattr"), [String
(Pathname, "path")], [];
@@ -9692,4 +9692,11 @@ C<guestfs_cryptsetup_open>. The C<device>
parameter must be
the name of the mapping device (ie. F</dev/mapper/mapname>)
and I<not> the name of the underlying block device." };
+ { defaults with
+ name = "internal_readdir"; added = (1, 48, 2);
+ style = RErr, [String (Pathname, "dir"); String (FileOut,
"filename")], [];
+ visibility = VInternal;
+ shortdesc = "read directories entries";
+ longdesc = "Internal function for readdir." };
+
]
diff --git a/generator/proc_nr.ml b/generator/proc_nr.ml
index b20672ff09aa..20e3db0bc78c 100644
--- a/generator/proc_nr.ml
+++ b/generator/proc_nr.ml
@@ -152,7 +152,7 @@ let proc_nr = [
135, "mknod_b";
136, "mknod_c";
137, "umask";
-138, "readdir";
+138, "internal_readdir";
139, "sfdiskM";
140, "zfile";
141, "getxattrs";
diff --git a/daemon/readdir.c b/daemon/readdir.c
index e488f93e727f..9ab0b0aec955 100644
--- a/daemon/readdir.c
+++ b/daemon/readdir.c
@@ -16,77 +16,67 @@
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301
USA.
*/
-#include <config.h>
+#include <config.h> /* HAVE_STRUCT_DIRENT_D_TYPE */
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
-#include <unistd.h>
-#include <dirent.h>
+#include <dirent.h> /* readdir() */
+#include <errno.h> /* errno */
+#include <rpc/xdr.h> /* xdrmem_create() */
+#include <stdio.h> /* perror() */
+#include <stdlib.h> /* malloc() */
+#include <sys/types.h> /* opendir() */
-#include "daemon.h"
-#include "actions.h"
+#include "daemon.h" /* reply_with_perror() */
-static void
-free_int_dirent_list (guestfs_int_dirent *p, size_t len)
+/* Has one FileOut parameter. */
+int
+do_internal_readdir (const char *dir)
{
- size_t i;
+ int ret;
+ DIR *dirstream;
+ void *xdr_buf;
+ XDR xdr;
- for (i = 0; i < len; ++i) {
- free (p[i].name);
- }
- free (p);
-}
-
-guestfs_int_dirent_list *
-do_readdir (const char *path)
-{
- guestfs_int_dirent_list *ret;
- guestfs_int_dirent v;
- DIR *dir;
- struct dirent *d;
- size_t i;
-
- ret = malloc (sizeof *ret);
- if (ret == NULL) {
- reply_with_perror ("malloc");
- return NULL;
- }
-
- ret->guestfs_int_dirent_list_len = 0;
- ret->guestfs_int_dirent_list_val = NULL;
+ /* Prepare to fail. */
+ ret = -1;
CHROOT_IN;
- dir = opendir (path);
+ dirstream = opendir (dir);
CHROOT_OUT;
- if (dir == NULL) {
- reply_with_perror ("opendir: %s", path);
- free (ret);
- return NULL;
+ if (dirstream == NULL) {
+ reply_with_perror ("opendir: %s", dir);
+ return ret;
}
- i = 0;
- while ((d = readdir (dir)) != NULL) {
- guestfs_int_dirent *p;
+ xdr_buf = malloc (GUESTFS_MAX_CHUNK_SIZE);
+ if (xdr_buf == NULL) {
+ reply_with_perror ("malloc");
+ goto close_dir;
+ }
+ xdrmem_create (&xdr, xdr_buf, GUESTFS_MAX_CHUNK_SIZE, XDR_ENCODE);
+
+ /* Send an "OK" reply, before starting the file transfer. */
+ reply (NULL, NULL);
+
+ /* From this point on, we can only report errors by canceling the file
+ * transfer.
+ */
+ for (;;) {
+ struct dirent *d;
+ guestfs_int_dirent v;
+
+ errno = 0;
+ d = readdir (dirstream);
+ if (d == NULL) {
+ if (errno == 0)
+ ret = 0;
+ else
+ perror ("readdir");
- p = realloc (ret->guestfs_int_dirent_list_val,
- sizeof (guestfs_int_dirent) * (i+1));
- v.name = strdup (d->d_name);
- if (!p || !v.name) {
- reply_with_perror ("allocate");
- if (p) {
- free_int_dirent_list (p, i);
- } else {
- free_int_dirent_list (ret->guestfs_int_dirent_list_val, i);
- }
- free (v.name);
- free (ret);
- closedir (dir);
- return NULL;
+ break;
}
- ret->guestfs_int_dirent_list_val = p;
+ v.name = d->d_name;
v.ino = d->d_ino;
#ifdef HAVE_STRUCT_DIRENT_D_TYPE
switch (d->d_type) {
@@ -104,19 +94,29 @@ do_readdir (const char *path)
v.ftyp = 'u';
#endif
- ret->guestfs_int_dirent_list_val[i] = v;
+ if (!xdr_guestfs_int_dirent (&xdr, &v)) {
+ fprintf (stderr, "xdr_guestfs_int_dirent failed\n");
+ break;
+ }
- i++;
+ if (send_file_write (xdr_buf, xdr_getpos (&xdr)) != 0)
+ break;
+
+ xdr_setpos (&xdr, 0);
}
- ret->guestfs_int_dirent_list_len = i;
+ /* Finish or cancel the transfer. Note that if (ret == -1) because the
library
+ * canceled, we still need to cancel back!
+ */
+ send_file_end (ret == -1);
- if (closedir (dir) == -1) {
- reply_with_perror ("closedir");
- free (ret->guestfs_int_dirent_list_val);
- free (ret);
- return NULL;
- }
+ xdr_destroy (&xdr);
+ free (xdr_buf);
+
+close_dir:
+ if (closedir (dirstream) == -1)
+ /* Best we can do here is log an error. */
+ perror ("closedir");
return ret;
}
diff --git a/lib/readdir.c b/lib/readdir.c
new file mode 100644
index 000000000000..9cb0d7cf6781
--- /dev/null
+++ b/lib/readdir.c
@@ -0,0 +1,131 @@
+/* libguestfs
+ * Copyright (C) 2016-2022 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> /* UNIX_PATH_MAX, needed by
"guestfs-internal.h" */
+
+#include <rpc/xdr.h> /* xdrstdio_create() */
+#include <stdint.h> /* UINT32_MAX */
+#include <stdio.h> /* fopen() */
+#include <string.h> /* memset() */
+
+#include "guestfs.h" /* guestfs_internal_readdir()
*/
+#include "guestfs_protocol.h" /* guestfs_int_dirent */
+#include "guestfs-internal.h" /* guestfs_int_make_temp_path()
*/
+#include "guestfs-internal-actions.h" /* guestfs_impl_readdir */
+
+struct guestfs_dirent_list *
+guestfs_impl_readdir (guestfs_h *g, const char *dir)
+{
+ struct guestfs_dirent_list *ret;
+ char *tmpfn;
+ FILE *f;
+ off_t fsize;
+ XDR xdr;
+ struct guestfs_dirent_list *dirents;
+ uint32_t alloc_entries;
+ size_t alloc_bytes;
+
+ /* Prepare to fail. */
+ ret = NULL;
+
+ tmpfn = guestfs_int_make_temp_path (g, "readdir", NULL);
+ if (tmpfn == NULL)
+ return ret;
+
+ if (guestfs_internal_readdir (g, dir, tmpfn) == -1)
+ goto drop_tmpfile;
+
+ f = fopen (tmpfn, "r");
+ if (f == NULL) {
+ perrorf (g, "fopen: %s", tmpfn);
+ goto drop_tmpfile;
+ }
+
+ if (fseeko (f, 0, SEEK_END) == -1) {
+ perrorf (g, "fseeko");
+ goto close_tmpfile;
+ }
+ fsize = ftello (f);
+ if (fsize == -1) {
+ perrorf (g, "ftello");
+ goto close_tmpfile;
+ }
+ if (fseeko (f, 0, SEEK_SET) == -1) {
+ perrorf (g, "fseeko");
+ goto close_tmpfile;
+ }
+
+ xdrstdio_create (&xdr, f, XDR_DECODE);
+
+ dirents = safe_malloc (g, sizeof *dirents);
+ dirents->len = 0;
+ alloc_entries = 8;
+ alloc_bytes = alloc_entries * sizeof *dirents->val;
+ dirents->val = safe_malloc (g, alloc_bytes);
+
+ while (xdr_getpos (&xdr) < fsize) {
+ guestfs_int_dirent v;
+ struct guestfs_dirent *d;
+
+ if (dirents->len == alloc_entries) {
+ if (alloc_entries > UINT32_MAX / 2 || alloc_bytes > (size_t)-1 / 2)
{
+ error (g, "integer overflow");
+ goto free_dirents;
+ }
+ alloc_entries *= 2u;
+ alloc_bytes *= 2u;
+ dirents->val = safe_realloc (g, dirents->val, alloc_bytes);
+ }
+
+ /* Decoding does not work unless the target buffer is zero-initialized. */
+ memset (&v, 0, sizeof v);
+ if (!xdr_guestfs_int_dirent (&xdr, &v)) {
+ error (g, "xdr_guestfs_int_dirent failed");
+ goto free_dirents;
+ }
+
+ d = &dirents->val[dirents->len];
+ d->ino = v.ino;
+ d->ftyp = v.ftyp;
+ d->name = v.name; /* transfer malloc'd string to "d" */
+
+ dirents->len++;
+ }
+
+ /* Success; transfer "dirents" to "ret". */
+ ret = dirents;
+ dirents = NULL;
+
+ /* Clean up. */
+ xdr_destroy (&xdr);
+
+free_dirents:
+ guestfs_free_dirent_list (dirents);
+
+close_tmpfile:
+ fclose (f);
+
+drop_tmpfile:
+ /* In case guestfs_internal_readdir() failed, it may or may not have created
+ * the temporary file.
+ */
+ unlink (tmpfn);
+ free (tmpfn);
+
+ return ret;
+}
diff --git a/TODO b/TODO
index a50f7d73c3dc..513e55f92eca 100644
--- a/TODO
+++ b/TODO
@@ -484,14 +484,6 @@ this approach works, it doesn't solve the MBR problem,
so likely we'd
have to write a library for that (or perhaps go back to sfdisk but
using a very abstracted interface over sfdisk).
-Reimplement some APIs to avoid protocol limits
-----------------------------------------------
-
-Mostly this item was done (eg. commits a69f44f56f and before). The
-most notable API with a protocol limit remaining is:
-
- - guestfs_readdir
-
hivex
-----
--
2.19.1.3.g30247aa5d201
Laszlo Ersek
2022-May-01 07:04 UTC
[Libguestfs] [libguestfs PATCH 2/2] guestfs_readdir(): minimize the number of send_file_write() calls
In guestfs_readdir(), the daemon currently sends each XDR-encoded
"guestfs_int_dirent" to the library with a separate send_file_write()
call.
Determine the largest encoded size (from the longest filename that a
"guestfs_int_dirent" could carry, from readdir()'s "struct
dirent"), and
batch up the XDR encodings until the next encoding might not fit in
GUESTFS_MAX_CHUNK_SIZE. Call send_file_write() only then.
Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1674392
Signed-off-by: Laszlo Ersek <lersek at redhat.com>
---
daemon/readdir.c | 38 ++++++++++++++++----
1 file changed, 32 insertions(+), 6 deletions(-)
diff --git a/daemon/readdir.c b/daemon/readdir.c
index 9ab0b0aec955..3084ba939c10 100644
--- a/daemon/readdir.c
+++ b/daemon/readdir.c
@@ -35,6 +35,9 @@ do_internal_readdir (const char *dir)
DIR *dirstream;
void *xdr_buf;
XDR xdr;
+ struct dirent fill;
+ guestfs_int_dirent v;
+ unsigned max_encoded;
/* Prepare to fail. */
ret = -1;
@@ -55,6 +58,20 @@ do_internal_readdir (const char *dir)
}
xdrmem_create (&xdr, xdr_buf, GUESTFS_MAX_CHUNK_SIZE, XDR_ENCODE);
+ /* Calculate the max number of bytes a "guestfs_int_dirent" can be
encoded to.
+ */
+ memset (fill.d_name, 'a', sizeof fill.d_name - 1);
+ fill.d_name[sizeof fill.d_name - 1] = '\0';
+ v.ino = INT64_MAX;
+ v.ftyp = '?';
+ v.name = fill.d_name;
+ if (!xdr_guestfs_int_dirent (&xdr, &v)) {
+ fprintf (stderr, "xdr_guestfs_int_dirent failed\n");
+ goto release_xdr;
+ }
+ max_encoded = xdr_getpos (&xdr);
+ xdr_setpos (&xdr, 0);
+
/* Send an "OK" reply, before starting the file transfer. */
reply (NULL, NULL);
@@ -63,7 +80,6 @@ do_internal_readdir (const char *dir)
*/
for (;;) {
struct dirent *d;
- guestfs_int_dirent v;
errno = 0;
d = readdir (dirstream);
@@ -94,22 +110,32 @@ do_internal_readdir (const char *dir)
v.ftyp = 'u';
#endif
+ /* Flush "xdr_buf" if we may not have enough room for encoding
"v". */
+ if (GUESTFS_MAX_CHUNK_SIZE - xdr_getpos (&xdr) < max_encoded) {
+ if (send_file_write (xdr_buf, xdr_getpos (&xdr)) != 0)
+ break;
+
+ xdr_setpos (&xdr, 0);
+ }
+
if (!xdr_guestfs_int_dirent (&xdr, &v)) {
fprintf (stderr, "xdr_guestfs_int_dirent failed\n");
break;
}
-
- if (send_file_write (xdr_buf, xdr_getpos (&xdr)) != 0)
- break;
-
- xdr_setpos (&xdr, 0);
}
+ /* Flush "xdr_buf" if the loop completed successfully and
"xdr_buf" is not
+ * empty. */
+ if (ret == 0 && xdr_getpos (&xdr) > 0 &&
+ send_file_write (xdr_buf, xdr_getpos (&xdr)) != 0)
+ ret = -1;
+
/* Finish or cancel the transfer. Note that if (ret == -1) because the
library
* canceled, we still need to cancel back!
*/
send_file_end (ret == -1);
+release_xdr:
xdr_destroy (&xdr);
free (xdr_buf);
--
2.19.1.3.g30247aa5d201