btl/vader: handle unexpected short read/write in process_vm_{read,wri… #4876
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…te}v Important note : According to the man page "On success, process_vm_readv() returns the number of bytes read and process_vm_writev() returns the number of bytes written. This return value may be less than the total number of requested bytes, if a partial read/write occurred. (Partial transfers apply at the granularity of iovec elements. These system calls won't perform a partial transfer that splits a single iovec element.)" So since we use a single iovec element, the returned size should either be 0 or size, and the do loop should not be needed here. We tried on various Linux kernels with size > 2 GB, and surprisingly, the returned value is always 0x7ffff000 (fwiw, it happens to be the size of the larger number of pages that fits a signed 32 bits integer). We do not know whether this is a bug from the kernel, the libc or even the man page, but for the time being, we do as is process_vm_readv() could return any value. Thanks Heiko Bauke for the bug report. Refs. open-mpi#4829 Signed-off-by: Gilles Gouaillardet <[email protected]> (cherry picked from commit open-mpi/ompi@9fedf28)
hjelmn
approved these changes
Mar 5, 2018
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…te}v
Important note :
According to the man page
"On success, process_vm_readv() returns the number of bytes read and
process_vm_writev() returns the number of bytes written. This return
value may be less than the total number of requested bytes, if a
partial read/write occurred. (Partial transfers apply at the
granularity of iovec elements. These system calls won't perform a
partial transfer that splits a single iovec element.)"
So since we use a single iovec element, the returned size should either
be 0 or size, and the do loop should not be needed here.
We tried on various Linux kernels with size > 2 GB, and surprisingly,
the returned value is always 0x7ffff000 (fwiw, it happens to be the size
of the larger number of pages that fits a signed 32 bits integer).
We do not know whether this is a bug from the kernel, the libc or even
the man page, but for the time being, we do as is process_vm_readv() could
return any value.
Thanks Heiko Bauke for the bug report.
Refs. #4829
Signed-off-by: Gilles Gouaillardet [email protected]
(cherry picked from commit 9fedf28)