libct/cg: introduce and use fscommon.OpenFile #2635
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Move the functionality of opening a cgroup file into a separate function, OpenFile, which, similar to ReadFile and WriteFile, use separate dir and file arguments. Change ReadFile and WriteFile to rely on OpenFile, and use lower-level read and write instead of ones from ioutil. It changes the semantics of WriteFile a bit -- it no longer uses O_CREAT flag. This is good for real cgroup as there is no need to try creating the files in there, but can potentially break WriteFile users -- previously, EPERM error was returned for non-existing files, and now it's ENOENT. This also breaks the fs/fs2 unit tests since they write to pseudo-cgroup files inside a test directory (not to a real cgroup fs), and now fscommon.WriteFile do not create or truncate files, so we have to add a variable that is set by the unit tests. Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
...and drop os.O_CREATE|os.O_TRUNC as those are definitely not needed. Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
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AkihiroSuda
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AkihiroSuda
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mrunalp
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Oct 23, 2020
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This is part III from #2598, preparing the code to use
openat2()Move the functionality of opening a cgroup file into a separate
function,
OpenFile, which, similar toReadFileandWriteFile,use separate dir and file arguments.
Change
ReadFileandWriteFileto rely onOpenFile, and use lower-levelread and write instead of ones from ioutil.
It changes the semantics of
WriteFilea bit -- it no longer usesO_CREATflag. This is good for real cgroup as there is no need to trycreating the files in there, but can potentially break WriteFile users
-- previously,
EPERMerror was returned for non-existing files, andnow it's
ENOENT.This also breaks the fs/fs2 unit tests since they write to pseudo-cgroup
files inside a test directory (not to a real cgroup fs), and now
fscommon.WriteFiledo not create or truncate files, so we have to add avariable that is set by the unit tests to emulate the old behavior.
Use the new interface where possible.