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gh-87909: avoid a 0 bytes copy call to sendfile() #101231

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gh-87909: avoid a 0 bytes copy call to sendfile() #101231

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8 changes: 6 additions & 2 deletions Lib/shutil.py
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Original file line number Diff line number Diff line change
Expand Up @@ -130,16 +130,20 @@ def _fastcopy_sendfile(fsrc, fdst):
# should not make any difference, also in case the file content
# changes while being copied.
try:
blocksize = max(os.fstat(infd).st_size, 2 ** 23) # min 8MiB
filesize = os.fstat(infd).st_size
blocksize = max(filesize, 2 ** 23) # min 8MiB
except OSError:
filesize = float("inf")
blocksize = 2 ** 27 # 128MiB
# On 32-bit architectures truncate to 1GiB to avoid OverflowError,
# see bpo-38319.
if sys.maxsize < 2 ** 32:
blocksize = min(blocksize, 2 ** 30)

offset = 0
while True:
# We explicitly limit ourselves to filesize to avoid odd behavior
# on some systems. https://github.com/python/cpython/issues/87909
while offset < filesize:
try:
sent = os.sendfile(outfd, infd, offset, blocksize)
except OSError as err:
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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Library/2023-01-21-18-31-09.gh-issue-87909.bn7V1p.rst
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@@ -0,0 +1,3 @@
Avoid an unusual case in :func:`shutil.copyfile` where the ``sendfile``
system call might return an error on some kernels and filesystems after all
data was transferred.
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