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Diffstat (limited to 'hurd/translator/tmpfs')
| -rw-r--r-- | hurd/translator/tmpfs/notes_various.mdwn | 201 |
1 files changed, 201 insertions, 0 deletions
diff --git a/hurd/translator/tmpfs/notes_various.mdwn b/hurd/translator/tmpfs/notes_various.mdwn new file mode 100644 index 00000000..e323a890 --- /dev/null +++ b/hurd/translator/tmpfs/notes_various.mdwn @@ -0,0 +1,201 @@ + <antrik> hde: what's the status on tmpfs? + <hde> Broke + <hde> k0ro traced the errors like the assert show above to a pager problem. + See the pager cannot handle request from multiple ports and tmpfs sends + request using two differ ports, so to fix it the pager needs to be hacked + to support multiple requests. + <hde> You can enable debugging in the pager by changing a line from dprintf + to ddprintf I can tell you how if you want. + <antrik> and changing tmpfs to use a single port isn't possible?... + <hde> antrik, I am not sure. + <hde> IIRC k0ro was saying it cannot be changed and I cannot recall his + reasons why. + <sdschulze> antrik: Doing it the quick&dirty way, I'd just use an N-ary + tree for representing the directory structure and mmap one new page (or + more) for each file. + <hde> sdschulze, What are you talking about? + <sdschulze> hde: about how I would implement tmpfs + <hde> O + <azeem> sdschulze: you don't need to reimplement it, just fix it :) + <sdschulze> azeem: Well, it seems a bit more difficult than I considered. + <sdschulze> I had assumed it was implemented the way I described. + <hde> O and the assert above gets triggered if you don't have a + default-pager setup on /servers/default-pager + <hde> the dir.c:62 assert that is. + <azeem> hde: you sure? I think I have one + <hde> I am almost sure. + <azeem> mbanck@beethoven:~$ showtrans /servers/default-pager + <azeem> /hurd/proxy-defpager + <azeem> isn't that enough? + <hde> It is suppose to be. + <hde> Try it as root + <hde> I was experiecing alot of bugs as a normal user, but according to + marcus it is suppose to work as root, but I was getting alot of hangs. + <azeem> hde: same issue, sudo doesn't work + <hde> sucky, well then there are alot of bugs. =) + <azeem> eh, no + <azeem> I still get the dir.c assert + <sdschulze> me too + <sdschulze> Without it, I already get an error message trying to set tmpfs + as an active translator. + +--- + + <hde> I think I found the colprit. + <hde> default_pager_object_set_size --> This is were tmpfs is hanging. + <hde> mmm Hangs on the message to the default-pager. + +--- + + <hde> Well it looks like tmpfs is sending a message to the default-pager, + the default-pager then receives the message and, checks the seqno. I + checked the mig gen code and noticed that the seqno is the reply port, it + this does not check out then the default pager is put into a what it + seems infinte condition_wait hoping to get the correct seqno. + <hde> Now I am figuring out how to fix it, and debugging some more. + +--- + + <marco_g> hde: Still working on tmpfs? + <hde> Yea + <marco_g> Did you fix a lot already? + <hde> No, just trying to narrow down the reason why we cannot write file + greater then 4.5K. + <marco_g> ahh + <marco_g> What did you figure out so far? + <hde> I used the quick marcus fix for the reading assert. + <marco_g> reading assert? + <hde> Yea you know ls asserted. + <marco_g> oh? :) + <hde> Because, the offsets changed in sturct dirent in libc. + <hde> They added 64 bit checks. + <hde> So marcus suggested a while ago on bug-hurd to just add some padding + arrays to the struct tmpfs_dirent. + <hde> And low and behold it works. + <marco_g> Oh, that fix. + <hde> Yup + <hde> marco_g, I have figured out that tmpfs sends a message to the + default-pager, the default-pager does receive the message, but then + checks the seqno(The reply port) and if it is not the same as the + default-pagers structure->seqno then she waits hoping to get the correct + one. Unfortantly it puts the pager into a infinite lock and never come + out of it. + <marco_g> hde: That sucks... + <marco_g> But at least you know what the problem is. + <hde> marco_g, Yea, now I am figuring out how to fix it. + <hde> Which requires more debugging lol. + <hde> There is also another bug, default_pager_object_set_size in + <hde> mach-defpager does never return when called and makes tmpfs hang. I + <hde> will have a closer look at this later this week. + +--- + + <hde> Cool, now that I have two pagers running, hopefully I will have less + system crashes. + <marcus> running more than one pager sounds like trouble to me, but maybe + hde means something different than I think + <hde> Well the other pager is only for tmpfs to use. + <hde> So I can debug the pager without messing with the entire system. + <hde> marcus, I am trying ti figure out why diskfs_object_set_size waits + forever. This way when the pager becomes locked forever I can turn it + off and restart it. When I was doing this with only one mach-defpager + running the system would crash. + <marcus> hde: how were you able to start two default pagers?? + <hde> Well you most likely will not think my way of doing it was correct, + and I am also not sure if it is lol. I made my hacked version not stop + working if one is alreay started. + +--- + + <hde> See, the default-pager has a function called + default_pager_object_set_size this sets the size for a memory object, + well it checks the seqno for each object if it is wrong it goes into a + condition_wait, and waits for another thread to give it a correct seqno, + well this never happens. + <hde> Thus, you get a hung tmpfs and default-pager. + <hde> pager_memcpy (pager=0x0, memobj=33, offset=4096, other=0x20740, + size=0x129df54, prot=3) at pager-memcpy.c:43 + <hde> bddebian, See the problem? + <bddebian> pager=0x0? + <hde> Yup + <hde> Now wtf is the deal, I must debug. + <hde> -- Function: struct pager * diskfs_get_filemap_pager_struct + <hde> (struct node *NP) + <hde> Return a `struct pager *' that refers to the pager returned by + <hde> diskfs_get_filemap for locked node NP, suitable for use as an + <hde> argument to `pager_memcpy'. + <hde> That is failing. + <hde> If it is not one thing it is another. + <bddebian> All of Mach fails ;-) + <hde> It is alot of work to make a test program that uses libdiskfs. + +--- + + <bing> to run tmpfs as a regular user, /servers/default-pager must be + executable by that user. by default it seems to be set to read/write. + <bing> $ sudo chmod ugo+x /servers/default-pager + <bing> you can see the O_EXEC in tmpfs.c + <bing> maybe this is just a debian packaging problem + <bing> it's probably a fix to native-install i'd guess + +--- + + <bing> tmpfs is failing on default_pager_object_create with -308, which + means server died + <bing> i'm running it as a regular user, so it gets it's pager from + /servers/default-pager + <bing> and showtrans /servers/default-pager shows /hurd/proxy-defpager + <bing> so i'm guessing that's the server that died + +--- + + <bing> this is about /hurd/tmpfs + <bing> a filesystem in memory + <bing> such that each file is it's own memory object + <andar> what does that mean exactly? it differs from a "ramdisk"? + <bing> instead of the whole fs being a memory object + <andar> it only allocates memory as needed? + <bing> each file is it's own + <bing> andar: yeah + <bing> it's not ext2 or anything + <andar> yea + <bing> it's tmpfs :-) + <bing> first off, echo "this" > that + <bing> fails + <bing> with a hang + <bing> on default_pager_object_create + <andar> so writing to the memory object fails + <bing> well, it's on the create + <andar> ah + <bing> and it returns -308 + <bing> which is server died + <bing> in mig-speak + <bing> but if i run it as root + <bing> things behave differently + <bing> it gets passed the create + <bing> but then i don't know what + <bing> i want to make it work for the regular user + <bing> it doesn't work as root either, it hangs elsewhere + <andar> but it at least creates the memory object + <bing> that's the braindump + <bing> but it's great for symlinks! + <andar> do you know if it creates it? + <bing> i could do stowfs in it + +--- + + <antrik> bing: k0ro (I think) analized the tmpfs problem some two years ago + or so, remember?... + <antrik> it turns out that it broke due to some change in other stuff + (glibc I think) + <antrik> problem was something like getting RPCs to same port from two + different sources or so + <antrik> and the fix to that is non-trivial + <antrik> I don't remember in what situations it broke exactly, maybe when + writing larger files? + <bing> antrik: yeah i never understood the explanation + <bing> antrik: right now it doesn't write any files + <bing> the change in glibc was to struct dirent + <antrik> seems something more broke in the meantime :-( + <antrik> ah, right... but I the main problem was some other change + <antrik> (or maybe it never really worked, not sure anymore) |