On Thu, Nov 21, 2019 at 8:28 AM Chen, Hu <hu1.chen@xxxxxxxxx> wrote: > > For Android application process, we found that the mnt_id read from > /proc/pid/fdinfo doesn't exist in /proc/pid/mountinfo. Thus CRIU fails > to dump such process and it complains > > "(00.019206) Error (criu/files-reg.c:1299): Can't lookup mount=42 for > fd=-3 path=/data/dalvik-cache/x86_64/system@framework@xxxxxxxx" > > This is due to how Android application is launched. In Android, there is > a special process called Zygote which handles the forking of each new > application process: > 0. Zygote opens and maps some files, for example > "/data/dalvik-cache/x86_64/system@framework@xxxxxxxx" in its current > mount namespace, say "old mnt ns". > 1. Zygote waits for the request to fork a new application. > 2. Zygote gets a request, it forks and run the new process in a new > mount namespace, say "new mnt ns". > > The file opened in step 0 ties to the mount point in "old mnt ns". The > mnt_id of that mount is listed in /proc/pid/fdinfo. However, > /proc/pid/mountinfo points to current ns, i.e., "new mnt ns". > > Althgouh this issue is exposed in Android, we believe it's generic. > Prcoess may open files and enter new mnt ns. > > To address it, this patch searches the mirror mount in current ns with > MAJOR and MINOR and shows the mirror's mnt_id. This is a hack. I suggest instead to add a new line to fdinfo with the MAJOR:MINOR number of the device. Thanks, Miklos
