On Fri, 15 Mar 2019 16:48:00 -0300, Arnaldo Carvalho de Melo wrote: > Em Fri, Mar 15, 2019 at 07:41:35PM +0000, Quentin Monnet escreveu: > > 2019-03-15 12:16 UTC-0700 ~ Jakub Kicinski <jakub.kicinski@xxxxxxxxxxxxx> > > > On Fri, 15 Mar 2019 15:41:41 -0300, Arnaldo Carvalho de Melo wrote: > > > > While developing 'perf trace' and looking at BPF maps it puts in place I > > > > noticed that one needs to first use 'bpftool map' to lookup a map id to > > > > then use 'bpftool map dump map id <map-id-looked-up>'. > > > > > > > > This is needed because everytime we restart 'perf trace' the map IDs > > > > gets changed so we need to do the ID lookup again. > > > > > > > > To speed up this sequence, allow specifying just the map name, look up > > > > its ID and then use the existing routines as if the user had provided > > > > the map id. > > > > > > I can see how it could be useful for quick debug. Names are not > > > guaranteed to be unique, though, do you not care about potential > > > duplicates? > > > > > > > Jakub beat me to it by a few seconds :). I discussed possible workarounds on > > that point with him though, so here are my two cents. I see two options: > > first one would be to return the ids of, and then dump info about all maps > > having that name. The second one would be to simply return an error if > > duplicate names are found. > > > > We agreed that returning an error if there are duplicates is probably the > > best way to go, because dealing with several maps for anything else than > > "bpftool map show" would be problematic (clearly, we don't want to update > > all maps with a given name at once). Of course if you have other > > suggestions, feel free to propose :). > > So, if there are dups, just tell that and print the ids, i.e. the > following, for any 'bpf map' command that finds dups, except for this > one: > > [root@quaco ~]# bpftool map list pids_filtered > 45: hash name pids_filtered flags 0x0 > key 4B value 1B max_entries 64 memlock 8192B > 90: hash name pids_filtered flags 0x0 > key 4B value 80B max_entries 512 memlock do-the-mathB > [root@quaco ~]# > > I.e. if there are multiple 'pids_filtered' maps, the output for, say, > 'dump' would be: > > [root@quaco ~]# bpftool map dump pids_filtered > There are multiple maps with this name, use 'bpftool map dump id NR' to disambiguate: > ------------------------------------------------------------------------------------- > 45: hash name pids_filtered flags 0x0 > key 4B value 1B max_entries 64 memlock 8192B > 90: hash name pids_filtered flags 0x0 > key 4B value 80B max_entries 512 memlock do-the-mathB > [root@quaco ~]# Yes, this looks good (modulo JSON output, which should probably be just a single "error" value). For simplicity I'd personally go for just always printing an error if name is duplicated and not bother with listing the options.
