Re: [Libguestfs] [v2v PATCH] RHV outputs: limit copied disk count to 23

On 06/17/22 11:17, Richard W.M. Jones wrote: > On Fri, Jun 17, 2022 at 11:08:52AM +0200, Laszlo Ersek wrote: >> We currently support virtio-blk (commonly) or IDE (unusually) for exposing >> disks to the converted guest; refer to "guestcaps.gcaps_block_bus" in >> "lib/create_ovf.ml". When using virtio-blk (i.e., in the common case), RHV >> can deal with at most 23 disks, as it plugs each virtio-blk device in a >> separate slot on the PCI(e) root bus; and the other slots are reserved for >> various purposes. When a domain has too many disks, the problem only >> becomes apparent once the copying finishes and an import is attempted. >> Modify the RHV outputs to fail relatively early when a domain has more >> than 23 disks that need to be copied. >> >> Notes: >> >> - With IDE, the theoretical limit may even be as low as 4. However, in the >> "Output_module.setup" function, we don't have access to >> "guestcaps.gcaps_block_bus", and in practice the IDE limitation has not >> caused surprises. So for now stick with 23, assuming virtio-blk. >> Modifying the "Output_module.setup" parameter list just for this seems >> overkill. >> >> - We could move the new check to an even earlier step, namely >> "Output_module.parse_options", due to the v2v directory deliberately >> existing (and having been populated with input sockets) at that time. >> However, even discounting the fact that "parse_options" is not a good >> name for including this kind of step, "parse_options" does not have >> access to the v2v directory name, and modifying the signature just for >> this is (again) overkill. >> >> - By adding the check to "Output_module.setup", we waste *some* effort >> (namely, the conversion occurs between "parse_options" and "setup"), >> but: (a) the "rhv-disk-uuid" count check (against the disk count) is >> already being done in the rhv-upload module's "setup" function, (b) in >> practice the slowest step ought to be the copying, and placing the new >> check in "setup" is early enough to prevent that. >> >> Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2051564 >> Signed-off-by: Laszlo Ersek <lersek(a)redhat.com&gt; >> --- >> >> Notes: >> This patch can be tested easily by replacing 23 with 0 in all three >> affected output modules -- then the following test cases all fail in >> "make check": >> >> FAIL: test-v2v-o-rhv.sh >> FAIL: test-v2v-o-vdsm-options.sh >> FAIL: test-v2v-o-rhv-upload.sh >> >> > [ 11.3] Setting up the destination: -o rhv >> > virt-v2v: error: this output module doesn't support copying more than 0 disks >> >> > [ 9.0] Setting up the destination: -o vdsm >> > virt-v2v: error: this output module doesn't support copying more than 0 disks >> >> > [ 11.2] Setting up the destination: -o rhv-upload -oc https://example.com/ovirt-engine/api -os Storage >> > virt-v2v: error: this output module doesn't support copying more than 0 disks >> >> output/output.mli | 7 +++++++ >> output/output.ml | 5 +++++ >> output/output_rhv.ml | 1 + >> output/output_rhv_upload.ml | 1 + >> output/output_vdsm.ml | 1 + >> 5 files changed, 15 insertions(+) >> >> diff --git a/output/output.mli b/output/output.mli >> index 533a0c51d31c..2dec8ccdc690 100644 >> --- a/output/output.mli >> +++ b/output/output.mli >> @@ -76,6 +76,13 @@ val get_disks : string -> (int * int64) list >> (** Examines the v2v directory and opens each input socket (in0 etc), >> returning a list of input disk index and size. *) >> >> +val bail_if_disk_count_gt : string -> int -> unit >> +(** This function lets an output module enforce a maximum disk count. >> + [bail_if_disk_count_gt dir n] checks whether the domain has more than [n] >> + disks that need to be copied, by examining the existence of input NBD socket >> + "in[n]" in the v2v directory [dir]. If the socket exists, [error] is >> + called. *) > > We've commonly called these types of functions "error_if_..." or > "error_unless_..." (you'll find many examples in the existing code). > Could be better to rename it that way for consistency. > >> val output_to_local_file : ?changeuid:((unit -> unit) -> unit) -> >> Types.output_allocation -> >> string -> string -> int64 -> string -> >> diff --git a/output/output.ml b/output/output.ml >> index 10e685c46926..0c4b437997d4 100644 >> --- a/output/output.ml >> +++ b/output/output.ml >> @@ -64,6 +64,11 @@ let get_disks dir = >> in >> loop [] 0 >> >> +let bail_if_disk_count_gt dir n = >> + let socket = sprintf "%s/in%d" dir n in >> + if Sys.file_exists socket then >> + error (f_"this output module doesn't support copying more than %d disks") n >> + >> let output_to_local_file ?(changeuid = fun f -> f ()) >> output_alloc output_format filename size socket = >> (* Check nbdkit is installed and has the required plugin. *) >> diff --git a/output/output_rhv.ml b/output/output_rhv.ml >> index 119207fdc065..a0c0be270755 100644 >> --- a/output/output_rhv.ml >> +++ b/output/output_rhv.ml >> @@ -56,6 +56,7 @@ module RHV = struct >> (options.output_alloc, options.output_format, output_name, output_storage) >> >> let rec setup dir options source = >> + bail_if_disk_count_gt dir 23; >> let disks = get_disks dir in >> let output_alloc, output_format, output_name, output_storage = options in >> >> diff --git a/output/output_rhv_upload.ml b/output/output_rhv_upload.ml >> index 828996b36261..6a9abf4eecdf 100644 >> --- a/output/output_rhv_upload.ml >> +++ b/output/output_rhv_upload.ml >> @@ -133,6 +133,7 @@ after their uploads (if you do, you must supply one for each disk): >> else PCRE.matches (Lazy.force rex_uuid) uuid >> >> let rec setup dir options source = >> + bail_if_disk_count_gt dir 23; >> let disks = get_disks dir in >> let output_conn, output_format, >> output_password, output_name, output_storage, >> diff --git a/output/output_vdsm.ml b/output/output_vdsm.ml >> index a1e8c2465810..02a2b5817fbc 100644 >> --- a/output/output_vdsm.ml >> +++ b/output/output_vdsm.ml >> @@ -119,6 +119,7 @@ For each disk you must supply one of each of these options: >> compat, ovf_flavour) >> >> let setup dir options source = >> + bail_if_disk_count_gt dir 23; >> let disks = get_disks dir in >> let output_alloc, output_format, >> output_name, output_storage, >> -- >> 2.19.1.3.g30247aa5d201 > > Looks fine, although I'd prefer the function to be renamed. Yes I will, consistency is important!