fs/poll: Fix poll_notify for CONFIG_BUILD_KERNEL #8072
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With flat addressing the user pollfd list is given directly to the drivers that perform the notification. This is fine when the addressing is flat, as there is no ambiguity on who gets notified and the fds memory is always mapped. For kernel mode with MMU this does not work. The notification must be done via a temporary buffer allocated from kernel memory. Thus, create a copy of the user fds and pass the copy to the drivers. Afterwards copy the output events back to the user.
xiaoxiang781216
approved these changes
Jan 10, 2023
| @@ -441,6 +441,7 @@ int file_poll(FAR struct file *filep, FAR struct pollfd *fds, bool setup) | |||
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| int poll(FAR struct pollfd *fds, nfds_t nfds, int timeout) | |||
| { | |||
| struct pollfd *kfds; | |||
pussuw
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Summary
With flat addressing the user pollfd list is given directly to the drivers that perform the notification. This is fine when the addressing is flat, as there is no ambiguity on who gets notified and the fds memory is always mapped.
For kernel mode with MMU this does not work. The notification must be done via a temporary buffer allocated from kernel memory.
Thus, create a copy of the user fds and pass the copy to the drivers. Afterwards copy the output events back to the user.
Impact
Fixes poll() for CONFIG_BUILD_KERNEL
Testing
icicle:knsh and in house risc-v target using CONFIG_BUILD_KERNEL