adb: fix adb usb operations on device.

Problem: For devices using /dev/usb-ffs/adb, Run
`while true; do adb reconnect device; sleep 1; done`. And the
device soon becomes offline. The adbd log shows that calling
adb_read(h->bulk_out) in usb_ffs_read() gets EOVERFLOW error.

Reason: When kicking a transport using usb-ffs, /dev/usb-ffs/adb/ep0
is not closed, and the device will not notify a usb connection reset
to host. So the host will continue to send unfinished packets even
if a new transport is started on device. The unfinished packets may
not have the same size as what is expected on device, so adbd on
device gets EOVERFLOW error. At the worst case, adbd has to create new
transports for each unfinished packet.

Fixes:
The direct fix is to make the usb connection reset when kicking transports,
as in https://android-review.googlesource.com/#/c/211267/1. And I think
we can make following improvements beside that.
1. Close a file that is used in other threads isn't safe. Because the file
descriptor may be reused to open other files, and other threads may operate
on the wrong file. So use dup2(dummy_fd) to replace close() in kick function,
and really close the file descriptor after the read/write threads exit.

2. Open new usb connection after usb_close() instead of after
usb_kick(). After usb_kick(), the transport may still exist and
reader/writer for the transport may be still running. But after
usb_close(), the previous transport is guaranteed to be destroyed.

Bug: 25935458
Change-Id: I1eff99662d1bf1cba66af7e7142f4c0c4d82c01b
(cherry picked from commit 005bf1e05be5de518184c376ebf88268bb191d09)

0 files changed, 0 insertions, 0 deletions