>>> Stephan Müller <smueller@xxxxxxxxxx> schrieb am 26.06.2017 um 19:38 in Nachricht <1678474.GnYBdSlWgs@xxxxxxxxxxxxxxxx>: > Am Montag, 26. Juni 2017, 03:23:09 CEST schrieb Nicholas A. Bellinger: > > Hi Nicholas, > >> Hi Stephan, Lee & Jason, >> >> (Adding target-devel CC') >> >> Apologies for coming late to the discussion. Comments below. >> >> On Sun, 2017-06-18 at 10:04 +0200, Stephan Müller wrote: >> > Am Samstag, 17. Juni 2017, 05:45:57 CEST schrieb Lee Duncan: >> > >> > Hi Lee, >> > >> > > In your testing, how long might a process have to wait? Are we talking >> > > seconds? Longer? What about timeouts? >> > >> > In current kernels (starting with 4.8) this timeout should clear within a >> > few seconds after boot. >> > >> > In older kernels (pre 4.8), my KVM takes up to 90 seconds to reach that >> > seeding point. I have heard that on IBM System Z this trigger point >> > requires minutes to be reached. >> >> I share the same concern as Lee wrt to introducing latency into the >> existing iscsi-target login sequence. >> >> Namely in the use-cases where a single node is supporting ~1K unique >> iscsi-target IQNs, and fail-over + re-balancing of IQNs where 100s of >> login attempts are expected to occur in parallel. >> >> If environments exist that require non trivial amounts of time for RNG >> seeding to be ready for iscsi-target usage, then enforcing this >> requirement at iscsi login time can open up problems, especially when >> iscsi host environments may be sensitive to login timeouts, I/O >> timeouts, et al. >> >> That said, I'd prefer to simply wait for RNG to be seeded at modprobe >> iscsi_target_mod time, instead of trying to enforce randomness during >> login. >> >> This way, those of use who have distributed storage platforms can know >> to avoid putting a node into a state to accept iscsi-target IQN export >> migration, before modprobe iscsi_target_mod has successfully loaded and >> RNG seeding has been confirmed. >> >> WDYT..? > > We may have a chicken and egg problem when the wait is at the modprobe time. > > Assume the modprobe happens during initramfs time to get access to the root > file system. In this case, you entire boot process will lock up for an > indefinite amount of time. The reason is that in order to obtain events > detected by the RNG, devices need to be initialized and working. Such > devices > commonly start working after the the root partition is mounted as it > contains > all drivers, all configuration information etc. > > Note, during the development of my /dev/random implementation, I added the > getrandom-like blocking behavior to /dev/urandom (which is the equivalent to > > Jason's patch except that it applies to user space). The boot process locked I thought reads from urandom never block by definition. An older manual page (man urandom) also says: "A read from the /dev/urandom device will not block waiting for more entropy." Regards, Ulrich > > up since systemd wanted data from /dev/urandom while it processed the > initramfs. As it did not get any, the boot process did not commence that > could > deliver new events to be picked up by the RNG. > > As I do not have such an iscsi system, I cannot test Jason's patch. But > maybe > the mentioned chicken-and-egg problem I mentioned above is already visible > with the current patch as it will lead to a blocking of the mounting of the > root partition in case the root partition is on an iscsi target. > > Ciao > Stephan > > -- > You received this message because you are subscribed to the Google Groups > "open-iscsi" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to open-iscsi+unsubscribe@xxxxxxxxxxxxxxxx. > To post to this group, send email to open-iscsi@xxxxxxxxxxxxxxxx. > Visit this group at https://groups.google.com/group/open-iscsi. > For more options, visit https://groups.google.com/d/optout.
