On Fri, Jun 07, 2013 at 11:29:31PM +0200, Daniel Stenberg wrote: > On Fri, 7 Jun 2013, Richard W.M. Jones wrote: > > >For a long time we've not been able to use Fedora's curl with > >qemu, but upstream curl from git just worked. A simple way to > >test this is to run: > > > > qemu-io http://libguestfs.org/index.html -c 'read -v 0 512' > > > >It will either print something or hang forever. > > Thanks for your detailed report and I also read your bugzilla entry > on this issue.
Thanks. > What exactly is that command line doing HTTP-wise? Is it "just" > asking for the first 512 bytes from that URL? If so, shouldn't the > plain curl command line tool also repeat the problem if it was truly > a pure libcurl problem? Well one thing we do know is that the curl CLI does *not* exhibit this problem. In other words, it doesn't seem to be a problem in curl. So either it's a bug in how qemu uses the curl API, or in qemu for some other reason (eg. coroutines, threads). I'll try to look into the items below when I have time, but it'd be great if you could just skip over the code here: http://git.qemu.org/?p=qemu.git;a=blob;f=block/curl.c;h=b8935fd9916363640df142d303b93756c8acf167;hb=HEAD and tell us if there's anything obviously broken about how it's using the API. (Note I didn't write any of it.) > Any chance you can try to write up a > smallish more plain libcurl-using code that can be used to attempt > to repeat the problem? > > Oh and btw, when it hangs, does it show it the resolver thread > function as the culprit in a gdb stack trace? No, it appears there is only one thread running when qemu / qemu-io goes to 100%: (gdb) t a a bt Thread 1 (Thread 0x7ffff7fb9880 (LWP 22558)): #0 g_array_remove_range (farray=farray@entry=0x555555c08230, index_=index_@entry=0, length=1) at garray.c:677 #1 0x00007ffff76cdd7c in g_array_set_size (farray=0x555555c08230, length=length@entry=0) at garray.c:556 #2 0x00005555555636df in aio_poll (ctx=0x555555c08020, blocking=blocking@entry=true) at aio-posix.c:200 #3 0x000055555559e989 in qemu_aio_wait () at main-loop.c:484 #4 0x000055555556ace5 in bdrv_rwv_co (bs=bs@entry=0x555555c123f0, sector_num=sector_num@entry=0, qiov=qiov@entry=0x7fffffffb7c0, is_write=is_write@entry=false) at block.c:2216 #5 0x000055555556ae80 in bdrv_rw_co (is_write=false, nb_sectors=<optimized out>, buf=<optimized out>, sector_num=0, bs= 0x555555c123f0) at block.c:2235 #6 bdrv_read (bs=bs@entry=0x555555c123f0, sector_num=sector_num@entry=0, buf=buf@entry=0x7fffffffbab0 "", nb_sectors=nb_sectors@entry=4) at block.c:2242 #7 0x000055555556b212 in bdrv_pread (bs=0x555555c123f0, offset=offset@entry= 0, buf=buf@entry=0x7fffffffbab0, count1=count1@entry=2048) at block.c:2304 #8 0x000055555556b900 in find_image_format (pdrv=<synthetic pointer>, filename=0x7fffffffe1d1 "http://192.168.0.249/scratch/winxp.img";, bs=<optimized out>) at block.c:542 #9 bdrv_open (bs=0x555555c0e9b0, filename=filename@entry= 0x7fffffffe1d1 "http://192.168.0.249/scratch/winxp.img";, options= 0x555555c103b0, options@entry=0x0, flags=24578, drv=drv@entry=0x0) at block.c:1055 #10 0x00005555555bb835 in openfile (growable=0, flags=<optimized out>, name= 0x7fffffffe1d1 "http://192.168.0.249/scratch/winxp.img";) at qemu-io.c:1812 #11 openfile (name=0x7fffffffe1d1 "http://192.168.0.249/scratch/winxp.img";, flags=<optimized out>, growable=<optimized out>) at qemu-io.c:1797 #12 0x0000555555563129 in main (argc=<optimized out>, argv=0x7fffffffde28) at qemu-io.c:2055 Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones virt-df lists disk usage of guests without needing to install any software inside the virtual machine. Supports Linux and Windows. http://people.redhat.com/~rjones/virt-df/ ------------------------------------------------------------------- List admin: http://cool.haxx.se/list/listinfo/curl-library Etiquette: http://curl.haxx.se/mail/etiquette.html
