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This patch is a rework of the NuttX file descriptor implementation. The goal is two-fold: 1. Improve POSIX compliance. The old implementation tied file description to inode only, not the file struct. POSIX however dictates otherwise. 2. Fix a bug with descriptor duplication (dup2() and dup3()). There is an existing race condition with this POSIX API that currently results in a kernel side crash. The crash occurs when a partially open / closed file descriptor is duplicated. The reason for the crash is that even if the descriptor is closed, the file might still be in use by the kernel (due to e.g. ongoing write to file). The open file data is changed by file_dup3() and this causes a crash in the device / drivers themselves as they lose access to the inode and private data. The fix is done by separating struct file into file and file descriptor structs. The file struct can live on even if the descriptor is closed, fixing the crash. This also fixes the POSIX issue, as two descriptors can now point to the same file. Signed-off-by: Ville Juven <ville.juven@unikie.com> Signed-off-by: dongjiuzhu1 <dongjiuzhu1@xiaomi.com>