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packages/pkg-download.mk: fix file locking over NFS

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BSD style locks such as implemented by flock are translated to POSIX
advisory file locks (implemented by the fcntl system call on Linux).  It
is not possible to lock a directory using POSIX advisory file locks.
Hence, the lock strategy used by Buildroot doesn't work when used over
NFS.

Using flock on a simple file works correctly though, so use a '.lock'
file inside the download directory instead. If the lockfile does not
exist, flock will create it (in a race-free fashion).

Tested using NFS v4.2 and Linux 5.4.43.

Signed-off-by: Maxim Cournoyer <maxim.cournoyer@savoirfairelinux.com>
[yann.morin.1998@free.fr:
  - slightly expand commit log about creation of the lockfile
]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
(cherry picked from commit 2e9d6565fc)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
This commit is contained in:
Maxim Cournoyer 2020-06-04 16:14:26 -04:00 committed by Peter Korsgaard
parent a842d033ac
commit b3554820a5
1 changed files with 1 additions and 1 deletions
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2
package/pkg-download.mk
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@ -99,7 +99,7 @@ endif
define DOWNLOAD
$(Q)mkdir -p $($(2)_DL_DIR)
$(Q)$(EXTRA_ENV) flock $($(2)_DL_DIR)/ $(DL_WRAPPER) \
$(Q)$(EXTRA_ENV) flock $($(2)_DL_DIR)/.lock $(DL_WRAPPER) \
-c '$($(2)_DL_VERSION)' \
-d '$($(2)_DL_DIR)' \
-D '$(DL_DIR)' \