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-rw-r--r--lib/libc/sys/open.27
1 files changed, 7 insertions, 0 deletions
diff --git a/lib/libc/sys/open.2 b/lib/libc/sys/open.2
index 769ac27..1a29a17 100644
--- a/lib/libc/sys/open.2
+++ b/lib/libc/sys/open.2
@@ -83,6 +83,7 @@ O_TRUNC truncate size to 0
O_EXCL error if create and file exists
O_SHLOCK atomically obtain a shared lock
O_EXLOCK atomically obtain an exclusive lock
+O_DIRECT eliminate or reduce cache effects
O_FSYNC synchronous writes
O_NOFOLLOW do not follow symlinks
.Ed
@@ -150,6 +151,12 @@ If creating a file with
the request for the lock will never fail
(provided that the underlying filesystem supports locking).
.Pp
+.Dv O_DIRECT may be used to
+minimize or eliminate the cache effects of reading and writing. The system
+will attempt to avoid caching the data you read or write. If it cannot
+avoid caching the data, it will minimize the impact the data has on the cache.
+Use of this flag can drastically reduce performance if not used with care.
+.Pp
If successful,
.Fn open
returns a non-negative integer, termed a file descriptor.
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