core/download: fix when the BR2_DL_DIR does not accept hardlinks
When the BR2_DL_DIR is a mountpoint (presumably shared between various machine, or mounted from the local host when running in a VM), it is possible that it does not support hardlinks (e.g. samba, or the VMWare VMFS, etc...). If the hardlink fails, fallback to copying the file. As a last resort, if that also fails, eventually fallback to doing the download. Note: this means that the dl-wrapper is no longer atomic-safe: the code suffers of a TOCTTOU condition: the file may be created in-between the check and the moment we try to ln/cp it. Fortunately, the dl-wrapper is now run under an flock, so we're still safe. If we eventually go for a more fine-grained implementation, we'll have to be careful then. Reported-by: Arnout Vandecappelle <arnout@mind.be> Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr> Cc: Arnout Vandecappelle <arnout@mind.be> Cc: Peter Korsgaard <peter@korsgaard.com> Cc: Maxime Hadjinlian <maxime.hadjinlian@gmail.com> Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
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@ -56,8 +56,13 @@ main() {
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# Legacy handling: check if the file already exists in the global
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# download directory. If it does, hard-link it. If it turns out it
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# was an incorrect download, we'd still check it below anyway.
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# If we can neither link nor copy, fallback to doing a download.
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# NOTE! This is not atomic, is subject to TOCTTOU, but the whole
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# dl-wrapper runs under an flock, so we're safe.
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if [ ! -e "${output}" -a -e "${old_dl_dir}/${filename}" ]; then
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ln "${old_dl_dir}/${filename}" "${output}"
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ln "${old_dl_dir}/${filename}" "${output}" || \
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cp "${old_dl_dir}/${filename}" "${output}" || \
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true
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fi
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# If the output file already exists and:
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