adding new O_* flags

Nicolas Thery nthery at
Sun Aug 2 07:37:52 PDT 2009


I'm trying to implement the new POSIX open(2) flags O_DIRECTORY,
O_SEARCH and O_EXEC described here:

I noticed that struct file.f_flags that stores the POSIX O_* flags and
some kernel internal ones has only one bit left (0x08000000).

I can see several options:

1/ Do not implement  O_DIRECTORY, O_SEARCH and O_EXEC (it doesn't seem
implemented (yet?) elsewhere).

2/ Use the single remaining bit for O_SEARCH and O_EXEC and overlay
O_DIRECTORY with some kernel internal bit.  Multiplexing O_SEARCH and
O_EXEC is fine because both involves checking the x permission bit
under the hood.  Overlaying O_DIRECTORY is fine too as it is only used
at open() time and does not need to be stored in f_flags.

3/ Extend f_flags to 64 bits, move all the kernel internal bits in the
most significant 32 bits and use the lower 32-bit for POSIX flags.

4/ Add a new internal flags int to struct file and move all kernel
internal bits here.

I favor either (3) or (2).

Do you have a preference?


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