[Libguestfs] [PATCH nbdkit v3] ssh: Allow the remote file to be created
Richard W.M. Jones
rjones at redhat.com
Tue Apr 19 09:14:55 UTC 2022
This adds new parameters, create=(true|false), create-size=SIZE and
create-mode=MODE to create and truncate the remote file.
---
plugins/ssh/nbdkit-ssh-plugin.pod | 34 ++++++++-
plugins/ssh/ssh.c | 112 +++++++++++++++++++++++++++---
tests/test-ssh.sh | 13 +++-
3 files changed, 146 insertions(+), 13 deletions(-)
diff --git a/plugins/ssh/nbdkit-ssh-plugin.pod b/plugins/ssh/nbdkit-ssh-plugin.pod
index 3f401c15..2bc2c4a7 100644
--- a/plugins/ssh/nbdkit-ssh-plugin.pod
+++ b/plugins/ssh/nbdkit-ssh-plugin.pod
@@ -5,8 +5,10 @@ nbdkit-ssh-plugin - access disk images over the SSH protocol
=head1 SYNOPSIS
nbdkit ssh host=HOST [path=]PATH
- [compression=true] [config=CONFIG_FILE] [identity=FILENAME]
- [known-hosts=FILENAME] [password=PASSWORD|-|+FILENAME]
+ [compression=true] [config=CONFIG_FILE]
+ [create=true] [create-mode=MODE] [create-size=SIZE]
+ [identity=FILENAME] [known-hosts=FILENAME]
+ [password=PASSWORD|-|+FILENAME]
[port=PORT] [timeout=SECS] [user=USER]
[verify-remote-host=false]
@@ -62,6 +64,34 @@ The C<config> parameter is optional. If it is I<not> specified at all
then F<~/.ssh/config> and F</etc/ssh/ssh_config> are both read.
Missing or unreadable files are ignored.
+=item B<create=true>
+
+(nbdkit E<ge> 1.32)
+
+If set, the remote file will be created. The remote file is created
+on the first NBD connection to nbdkit, not when nbdkit starts up. If
+the file already exists, it will be replaced and any existing content
+lost.
+
+If using this option, you must use C<create-size>. C<create-mode> can
+be used to control the permissions of the new file.
+
+=item B<create-mode=>MODE
+
+(nbdkit E<ge> 1.32)
+
+If using C<create=true> specify the default permissions of the new
+remote file. You can use octal modes like C<create-mode=0777> or
+C<create-mode=0644>. The default is C<0600>, ie. only readable and
+writable by the remote user.
+
+=item B<create-size=>SIZE
+
+(nbdkit E<ge> 1.32)
+
+If using C<create=true>, specify the virtual size of the new disk.
+C<SIZE> can use modifiers like C<100M> etc.
+
=item B<host=>HOST
Specify the name or IP address of the remote host.
diff --git a/plugins/ssh/ssh.c b/plugins/ssh/ssh.c
index 77cfcf6c..ac9cc230 100644
--- a/plugins/ssh/ssh.c
+++ b/plugins/ssh/ssh.c
@@ -44,12 +44,15 @@
#include <fcntl.h>
#include <sys/stat.h>
+#include <pthread.h>
+
#include <libssh/libssh.h>
#include <libssh/sftp.h>
#include <libssh/callbacks.h>
#include <nbdkit-plugin.h>
+#include "cleanup.h"
#include "const-string-vector.h"
#include "minmax.h"
@@ -63,6 +66,9 @@ static const char *known_hosts = NULL;
static const_string_vector identities = empty_vector;
static uint32_t timeout = 0;
static bool compression = false;
+static bool create = false;
+static int64_t create_size = -1;
+static unsigned create_mode = S_IRUSR | S_IWUSR /* 0600 */;
/* config can be:
* NULL => parse options from default file
@@ -167,6 +173,27 @@ ssh_config (const char *key, const char *value)
return -1;
compression = r;
}
+ else if (strcmp (key, "create") == 0) {
+ r = nbdkit_parse_bool (value);
+ if (r == -1)
+ return -1;
+ create = r;
+ }
+ else if (strcmp (key, "create-size") == 0) {
+ create_size = nbdkit_parse_size (value);
+ if (create_size == -1)
+ return -1;
+ }
+ else if (strcmp (key, "create-mode") == 0) {
+ r = nbdkit_parse_unsigned (key, value, &create_mode);
+ if (r == -1)
+ return -1;
+ /* OpenSSH checks this too. */
+ if (create_mode > 0777) {
+ nbdkit_error ("create-mode must be <= 0777");
+ return -1;
+ }
+ }
else {
nbdkit_error ("unknown parameter '%s'", key);
@@ -186,6 +213,13 @@ ssh_config_complete (void)
return -1;
}
+ /* If create=true, create-size must be supplied. */
+ if (create && create_size == -1) {
+ nbdkit_error ("if using create=true, you must specify the size "
+ "of the new remote file using create-size=SIZE");
+ return -1;
+ }
+
return 0;
}
@@ -200,7 +234,10 @@ ssh_config_complete (void)
"identity=<FILENAME> Prepend private key (identity) file.\n" \
"timeout=SECS Set SSH connection timeout.\n" \
"verify-remote-host=false Ignore known_hosts.\n" \
- "compression=true Enable compression."
+ "compression=true Enable compression.\n" \
+ "create=true Create the remote file.\n" \
+ "create-mode=MODE Set the permissions of the remote file.\n" \
+ "create-size=SIZE Set the size of the remote file."
/* Since we must simulate atomic pread and pwrite using seek +
* read/write, calls on each handle must be serialized.
@@ -329,6 +366,65 @@ authenticate (struct ssh_handle *h)
return -1;
}
+/* This function opens or creates the remote file (depending on
+ * create=false|true). Parallel connections might call this function
+ * at the same time, and so we must hold a lock to ensure that the
+ * file is created at most once.
+ */
+static pthread_mutex_t create_lock = PTHREAD_MUTEX_INITIALIZER;
+
+static sftp_file
+open_or_create_path (ssh_session session, sftp_session sftp, int readonly)
+{
+ ACQUIRE_LOCK_FOR_CURRENT_SCOPE (&create_lock);
+ int access_type;
+ int r;
+ sftp_file file;
+
+ access_type = readonly ? O_RDONLY : O_RDWR;
+ if (create) access_type |= O_CREAT | O_TRUNC;
+
+ file = sftp_open (sftp, path, access_type, S_IRWXU);
+ if (!file) {
+ nbdkit_error ("cannot %s file for %s: %s",
+ create ? "create" : "open",
+ readonly ? "reading" : "writing",
+ ssh_get_error (session));
+ return NULL;
+ }
+
+ if (create) {
+ /* There's no sftp_truncate call. However OpenSSH lets you call
+ * SSH_FXP_SETSTAT + SSH_FILEXFER_ATTR_SIZE which invokes
+ * truncate(2) on the server. Libssh doesn't provide a binding
+ * for SSH_FXP_FSETSTAT so we have to pass the session + path.
+ */
+ struct sftp_attributes_struct attrs = {
+ .flags = SSH_FILEXFER_ATTR_SIZE |
+ SSH_FILEXFER_ATTR_PERMISSIONS,
+ .size = create_size,
+ .permissions = create_mode,
+ };
+
+ r = sftp_setstat (sftp, path, &attrs);
+ if (r != SSH_OK) {
+ nbdkit_error ("setstat failed: %s", ssh_get_error (session));
+
+ /* Best-effort attempt to delete the remote file on failure. */
+ r = sftp_unlink (sftp, path);
+ if (r != SSH_OK)
+ nbdkit_debug ("unlink failed: %s", ssh_get_error (session));
+
+ return NULL;
+ }
+ }
+
+ /* On the next connection, don't create or truncate the file. */
+ create = false;
+
+ return file;
+}
+
/* Create the per-connection handle. */
static void *
ssh_open (int readonly)
@@ -337,7 +433,6 @@ ssh_open (int readonly)
const int set = 1;
size_t i;
int r;
- int access_type;
h = calloc (1, sizeof *h);
if (h == NULL) {
@@ -471,7 +566,7 @@ ssh_open (int readonly)
if (authenticate (h) == -1)
goto err;
- /* Open the SFTP connection and file. */
+ /* Open the SFTP connection. */
h->sftp = sftp_new (h->session);
if (!h->sftp) {
nbdkit_error ("failed to allocate sftp session: %s",
@@ -484,14 +579,11 @@ ssh_open (int readonly)
ssh_get_error (h->session));
goto err;
}
- access_type = readonly ? O_RDONLY : O_RDWR;
- h->file = sftp_open (h->sftp, path, access_type, S_IRWXU);
- if (!h->file) {
- nbdkit_error ("cannot open file for %s: %s",
- readonly ? "reading" : "writing",
- ssh_get_error (h->session));
+
+ /* Open or create the remote file. */
+ h->file = open_or_create_path (h->session, h->sftp, readonly);
+ if (!h->file)
goto err;
- }
nbdkit_debug ("opened libssh handle");
diff --git a/tests/test-ssh.sh b/tests/test-ssh.sh
index 6c0ce410..f04b4488 100755
--- a/tests/test-ssh.sh
+++ b/tests/test-ssh.sh
@@ -36,6 +36,7 @@ set -x
requires test -f disk
requires nbdcopy --version
+requires stat --version
# Check that ssh to localhost will work without any passwords or phrases.
#
@@ -48,7 +49,7 @@ then
exit 77
fi
-files="ssh.img"
+files="ssh.img ssh2.img"
rm -f $files
cleanup_fn rm -f $files
@@ -59,3 +60,13 @@ nbdkit -v -D ssh.log=2 -U - \
# The output should be identical.
cmp disk ssh.img
+
+# Copy local file 'ssh.img' to newly created "remote" 'ssh2.img'
+size="$(stat -c %s disk)"
+nbdkit -v -D ssh.log=2 -U - \
+ ssh host=localhost $PWD/ssh2.img \
+ create=true create-size=$size \
+ --run 'nbdcopy ssh.img "$uri"'
+
+# The output should be identical.
+cmp disk ssh2.img
--
2.35.1
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