[INCOMPLETE PATCH nbdkit] ssh: Allow the remote file to be created
This patch is incomplete (missing tests) so for discussion only, but it implements nbdkit-ssh-plugin create=true option which creates the remote file. Example: $ nbdkit ssh host=foo /var/tmp/newdisk create=true create-size=100M $ nbdsh -u nbd://localhost The disk is only created on first connection (which works the same way as nbdkit-vddk-plugin). So if you just want to create the remote disk and not do anything else, you should do something like this: nbdkit -U - ssh host=foo /var/tmp/newdisk create=true create-size=100M \ --run 'nbdinfo --can connect $uri' If the remote disk already exists, it is truncated but not recreated (in this case you'll notice the remote ctime is not touched). For some reason I don't understand, create-mode=0777 is ineffective. sftp-server has a -u option to set the umask, or else it uses the remote user's umask. I verified that openssh does *not* use the -u option and that the umask of sftp-server is 0002, yet the permissions on the file are still 0700. Rich.
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 | 37 +++++++++++++++++-- plugins/ssh/ssh.c | 60 +++++++++++++++++++++++++++++-- 2 files changed, 93 insertions(+), 4 deletions(-) diff --git a/plugins/ssh/nbdkit-ssh-plugin.pod b/plugins/ssh/nbdkit-ssh-plugin.pod index 3f401c15..648fa94d 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 +64,37 @@ 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 if it does not exist already. +Note the remote file is created on first NBD connection to nbdkit. + +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>. The +default is C<0600>, ie. only readable and writable by the remote user. + +The SFTP server may apply a L<umask(2)> which is specific to the +remote system and cannot be queried from the client, so the final +permissions may be more restrictive than requested. For OpenSSH I +found that files are always created with mode & 0700 whatever mode is +specified here, but other servers might be different. + +=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 3b2b21c8..66998813 100644 --- a/plugins/ssh/ssh.c +++ b/plugins/ssh/ssh.c @@ -63,6 +63,9 @@ 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 +170,27 @@ 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 +210,13 @@ 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 +231,10 @@ 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." /* The per-connection handle. */ struct ssh_handle { @@ -480,7 +514,8 @@ ssh_open (int readonly) goto err; } access_type = readonly ? O_RDONLY : O_RDWR; - h->file = sftp_open (h->sftp, path, access_type, S_IRWXU); + if (create) access_type |= O_CREAT; + h->file = sftp_open (h->sftp, path, access_type, create_mode); if (!h->file) { nbdkit_error ("cannot open file for %s: %s", readonly ? "reading" : "writing", @@ -488,6 +523,27 @@ ssh_open (int readonly) goto err; } + 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, + .size = create_size, + }; + + r = sftp_setstat (h->sftp, path, &attrs); + if (r != SSH_OK) { + nbdkit_error ("truncate failed: %s", ssh_get_error (h->session)); + goto err; + } + } + + /* On the next open, don't create or truncate the file. */ + create = false; + nbdkit_debug ("opened libssh handle"); return h; -- 2.35.1
participants (1)
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Richard W.M. Jones