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c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1674252376; h=from:from:sender:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:list-id:list-help: list-unsubscribe:list-subscribe:list-post; bh=5eaXoU6gWsMARdrTQwimbct6v9jYFv+PqeaAD588CfU=; b=XKZfCQFVON46Cj9BmYwSalUJNJrh0HQQTcfcrOxfIRw1hDwrthSVjXT565NVWX99TCXoux wA8MZuiu5yfFCooYw5FBS6xX1Rro5p4A/D98kLBMWKNFeZwmN+fXyzKMAvkE0sTiQRATfk JsOg35hix1cxD/L/b0MTENmmNcjM1Wg= X-MC-Unique: hO5jyOA4Nzu002xRD9R9CQ-1 X-Original-To: libvir-list@listman.corp.redhat.com From: Jonathon Jongsma To: libvir-list@redhat.com Subject: [libvirt PATCH v4 25/31] qemu: try to connect to nbdkit early to detect errors Date: Fri, 20 Jan 2023 16:03:19 -0600 Message-Id: <20230120220325.1015090-26-jjongsma@redhat.com> In-Reply-To: <20230120220325.1015090-1-jjongsma@redhat.com> References: <20230120220325.1015090-1-jjongsma@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.7 X-BeenThere: libvir-list@redhat.com X-Mailman-Version: 2.1.29 Precedence: list List-Id: Development discussions about the libvirt library & tools List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: libvir-list-bounces@redhat.com Sender: "libvir-list" X-Scanned-By: MIMEDefang 3.1 on 10.11.54.6 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: quoted-printable X-ZohoMail-DKIM: pass (identity @redhat.com) X-ZM-MESSAGEID: 1674252377895100001 Content-Type: text/plain; charset="utf-8"; x-default="true" When using nbdkit to serve a network disk source, the nbdkit process will start and wait for an nbd connection before actually attempting to connect to the (remote) disk location. Because of this, nbdkit will not report an error until after qemu is launched and tries to read from the disk. This results in a fairly user-unfriendly error saying that qemu was unable to start because "Requested export not available". Ideally we'd like to be able to tell the user *why* the export is not available, but this sort of information is only available to nbdkit, not qemu. It could be because the url was incorrect, or because of an authentication failure, or one of many other possibilities. To make this friendlier for users and easier to detect misconfigurations, try to connect to nbdkit immediately after starting nbdkit and before we try to start qemu. This requires adding a dependency on libnbd. If an error occurs when connecting to nbdkit, read back from the nbdkit error log and provide that information in the error report from qemuNbdkitProcessStart(). User-visible change demonstrated below: Previous error: $ virsh start nbdkit-test 2023-01-18 19:47:45.778+0000: 30895: error : virNetClientProgramDispatc= hError:172 : internal error: process exited while connecting to monitor: 2023-01-18T19:47:45.= 704658Z qemu-system-x86_64: -blockdev {"driver":"nbd","server":{"type":"unix", "path":"/var/lib/libvirt/qemu/domain-1-nbdkit-test/nbdkit-libvirt-1-sto= rage.socket"}, "node-name":"libvirt-1-storage","auto-read-only":true,"discard":"unmap"= }: Requested export not available error: Failed to start domain 'nbdkit-test' error: internal error: process exited while connecting to monitor: 2023= -01-18T19:47:45.704658Z qemu-system-x86_64: -blockdev {"driver":"nbd","server":{"type":"unix", "path":"/var/lib/libvirt/qemu/domain-1-nbdkit-test/nbdkit-libvirt-1-sto= rage.socket"}, "node-name":"libvirt-1-storage","auto-read-only":true,"discard":"unmap"= }: Requested export not available After this change: $ virsh start nbdkit-test 2023-01-18 19:44:36.242+0000: 30895: error : virNetClientProgramDispatc= hError:172 : internal error: Failed to connect to nbdkit for 'http://localhost:8888/nonexiste= nt.iso': nbdkit: curl[1]: error: problem doing HEAD request to fetch size of URL [http://localhos= t:8888/nonexistent.iso]: HTTP response code said error: The requested URL returned error: 404 error: Failed to start domain 'nbdkit-test' error: internal error: Failed to connect to nbdkit for 'http://localhos= t:8888/nonexistent.iso]: error: problem doing HEAD request to fetch size of URL [http://localhos= t:8888/nonexistent.iso]: HTTP response code said error: The requested URL returned error: 404 Signed-off-by: Jonathon Jongsma --- meson.build | 7 +++++++ meson_options.txt | 1 + src/qemu/meson.build | 1 + src/qemu/qemu_nbdkit.c | 24 ++++++++++++++++++++++++ 4 files changed, 33 insertions(+) diff --git a/meson.build b/meson.build index 048b15ff71..83692bef22 100644 --- a/meson.build +++ b/meson.build @@ -959,6 +959,12 @@ endif libiscsi_version =3D '1.18.0' libiscsi_dep =3D dependency('libiscsi', version: '>=3D' + libiscsi_version= , required: get_option('libiscsi')) =20 +libnbd_version =3D '1.0' +libnbd_dep =3D dependency('libnbd', version: '>=3D' + libnbd_version, requ= ired: get_option('libnbd')) +if libnbd_dep.found() + conf.set('WITH_LIBNBD', 1) +endif + libnl_version =3D '3.0' if not get_option('libnl').disabled() and host_machine.system() =3D=3D 'li= nux' libnl_dep =3D dependency('libnl-3.0', version: '>=3D' + libnl_version, r= equired: get_option('libnl')) @@ -2200,6 +2206,7 @@ libs_summary =3D { 'glusterfs': glusterfs_dep.found(), 'libiscsi': libiscsi_dep.found(), 'libkvm': libkvm_dep.found(), + 'libnbd': libnbd_dep.found(), 'libnl': libnl_dep.found(), 'libparted': libparted_dep.found(), 'libpcap': libpcap_dep.found(), diff --git a/meson_options.txt b/meson_options.txt index 861c5577d2..2d68bd7349 100644 --- a/meson_options.txt +++ b/meson_options.txt @@ -24,6 +24,7 @@ option('curl', type: 'feature', value: 'auto', descriptio= n: 'curl support') option('fuse', type: 'feature', value: 'auto', description: 'fuse support') option('glusterfs', type: 'feature', value: 'auto', description: 'glusterf= s support') option('libiscsi', type: 'feature', value: 'auto', description: 'libiscsi = support') +option('libnbd', type: 'feature', value: 'auto', description: 'libnbd supp= ort') option('libnl', type: 'feature', value: 'auto', description: 'libnl suppor= t') option('libpcap', type: 'feature', value: 'auto', description: 'libpcap su= pport') option('libssh', type: 'feature', value: 'auto', description: 'libssh supp= ort') diff --git a/src/qemu/meson.build b/src/qemu/meson.build index 6d7a1bfbb0..607b597c8c 100644 --- a/src/qemu/meson.build +++ b/src/qemu/meson.build @@ -99,6 +99,7 @@ if conf.has('WITH_QEMU') access_dep, capng_dep, gnutls_dep, + libnbd_dep, libnl_dep, log_dep, selinux_dep, diff --git a/src/qemu/qemu_nbdkit.c b/src/qemu/qemu_nbdkit.c index 934970e68c..98f8b70391 100644 --- a/src/qemu/qemu_nbdkit.c +++ b/src/qemu/qemu_nbdkit.c @@ -19,6 +19,9 @@ =20 #include #include +#if WITH_LIBNBD +# include +#endif #include =20 #include "vircommand.h" @@ -26,6 +29,7 @@ #include "virevent.h" #include "virlog.h" #include "virpidfile.h" +#include "virstring.h" #include "virtime.h" #include "virutil.h" #include "qemu_block.h" @@ -1190,6 +1194,9 @@ qemuNbdkitProcessStart(qemuNbdkitProcess *proc, g_autofree char *errmsg =3D NULL; g_autoptr(virURI) uri =3D NULL; g_autofree char *uristring =3D NULL; +#if WITH_LIBNBD + struct nbd_handle *nbd =3D NULL; +#endif =20 if (!(cmd =3D qemuNbdkitProcessBuildCommand(proc))) return -1; @@ -1240,6 +1247,23 @@ qemuNbdkitProcessStart(qemuNbdkitProcess *proc, goto error; } =20 +#if WITH_LIBNBD + /* if the disk source was misconfigured, nbdkit will not produce an er= ror + * until somebody connects to the socket and tries to access the nbd + * export. This results in poor user experience because the only error= we + * would get from qemu is something like "Requested export not availab= le". + * So let's try to access it ourselves so that we can error out early = and + * provide a useful message to the user. + */ + nbd =3D nbd_create(); + if (nbd_connect_unix(nbd, proc->socketfile) < 0) { + VIR_WARN("nbd_connect_unix failed: %s", nbd_get_error()); + nbd_close(nbd); + goto error; + } + nbd_close(nbd); +#endif + if (qemuNbdkitProcessStartMonitor(proc, vm) < 0) goto error; =20 --=20 2.39.0