Re: [Libguestfs] [PATCH nbdkit] server: Deprecate the -e/--exportname parameter.

On 7/22/20 4:02 AM, Richard W.M. Jones wrote: >Perhaps we should have a rule something like this: > > - plugins should serve default content on the "" export > > - unless they implement .list_exports, in which case the > first export returned is the default export That could be expensive, reading the entire list and throwing away all but the first. I'm now leaning towards two callbacks: .list_exports: compute all exports to advertise .default_export: compute the name to be returned for NBD_OPT_INFO("") and to use by default as $exportname in --run

Then, any plugin that wants to advertise a different default export name supplies .default_export, and if .default_export is missing, we supply "" on their behalf. We could also translate a client request for "" into .default_export before calling .open (v3) or populating nbdkit_export_name (v2) (I could see that mattering for the file plugin with a mode that serves all files in a directory, since stat("") fails but providing a default filename as the largest file in the directory could be useful). >Then we could implement --run transparently by having it set >$exportname/$uri to the first entry in .list_exports or "" if >.list_exports is not implemented. > >Here's another idea: Is it possible that if the --run script itself >overrides exportname it could be used by $uri. Not sure if there's >some kind of delayed shell variable expansion that would make this >possible: > > nbdkit ... --run 'exportname=foo; nbdsh -u $uri ...' Not as written, but we _can_ do the following. Right now, --run creates a shell fragment, which prepends this code in front of the user's: uri=... nbd=... ... exportname=... we could instead prepend: set_export() { uri=... nbd=... ... exportname=$1 } set_export ... where that last line uses .default_export (defaulting to "" as usual). The user can now run: nbdkit ... --run 'set_export foo; nbdsh -u "$uri" ... '

Oh, and I just realized, because $uri can contain ?, we really should scrub all uses in the tree to always write it as "$uri" rather than unquoted, just to set a good example. (It's unlikely that anyone would ever have a subdirectory named 'nbd+unix:' in their current working directory to the point that the ? would trigger unintended globbing, but better safe than sorry...)