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Give a bit more background on "uapi headers".

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Not everyone knows what these are, and we don't otherwise explain it.

Test: N/A
Change-Id: Ic28e4fd0f8584f5e808ab60f0c2e68dd0cf30088
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Elliott Hughes 2024-01-11 00:09:25 +00:00
parent a4d60ad5a2
commit cfc3090868
1 changed files with 23 additions and 6 deletions
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README.md
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@ -85,12 +85,29 @@ libc/
# files written by us and files taken from BSD.
kernel/
# The kernel uapi header files. These are scrubbed copies of the originals
# in external/kernel-headers/. These files must not be edited directly. The
# generate_uapi_headers.sh script should be used to go from a kernel tree to
# external/kernel-headers/ --- this takes care of the architecture-specific
# details. The update_all.py script should be used to regenerate bionic's
# scrubbed headers from external/kernel-headers/.
# The kernel uapi header files. The "libc" headers that developers actually
# use are a mixture of headers provided by the C library itself (which,
# for bionic, are in bionic/libc/include/) and headers provided by the
# kernel. This is because ISO C and POSIX will say things like "there is
# a constant called PROT_NONE" or "there is a type called struct stat,
# and it contains a field called st_size", but they won't necessarily say
# what _value_ that constant has, or what _order_ the fields in a type
# are in. Those are left to individual kernels' ABIs. In an effort to --
# amongst other things, see https://lwn.net/Articles/507794/ for more
# background -- reduce copy & paste, the Linux kernel makes all the types
# and constants that make up the "userspace API" (uapi) available as
# headers separate from their internal-use headers (which contain all kinds
# of extra stuff that isn't available to userspace). We import the latest
# released kernel's uapi headers in external/kernel-headers/, but we don't
# use those headers directly in bionic. The bionic/libc/kernel/ directory
# contains scrubbed copies of the originals from external/kernel-headers/.
# The generate_uapi_headers.sh script should be used to go from a kernel
# tree to external/kernel-headers/ --- this takes care of the
# architecture-specific details. The update_all.py script should then be
# used to regenerate bionic's copy from external/kernel-headers/.
# The files in bionic must not be edited directly because any local changes
# will be overwritten by the next update. "Updating kernel header files"
# below has more information on this process.
private/
# These are private header files meant for use within bionic itself.