mirror of https://github.com/mkerrisk/man-pages
memfd_create.2: Add description of MFD_HUGETLB (hugetlbfs) support
hugetlbfs support for memfd_create() was recently merged by Linus and should be in the Linux 4.14 release. To request hugetlbfs support a new memfd_create() flag (MFD_HUGETLB) was added. This patch documents the following commit: commit 749df87bd7bee5a79cef073f5d032ddb2b211de8 Author: Mike Kravetz <mike.kravetz@oracle.com> Date: Wed Sep 6 16:24:16 2017 -0700 mm/shmem: add hugetlbfs support to memfd_create() Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com> Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
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@ -100,6 +100,33 @@ If this flag is not set, the initial set of seals will be
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meaning that no other seals can be set on the file.
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meaning that no other seals can be set on the file.
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.\" FIXME Why is the MFD_ALLOW_SEALING behavior not simply the default?
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.\" FIXME Why is the MFD_ALLOW_SEALING behavior not simply the default?
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.\" Is it worth adding some text explaining this?
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.\" Is it worth adding some text explaining this?
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.TP
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.BR MFD_HUGETLB " (since Linux 4.14)"
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The anonymous file will be created in the hugetlbfs filesystem using
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huge pages. See the Linux kernel source file
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.I Documentation/vm/hugetlbpage.txt
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for more information about hugetlbfs. The hugetlbfs filesystem does
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not support file sealing operations. Therefore, specifying both
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.B MFD_HUGETLB
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and
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.B MFD_ALLOW_SEALING
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will result in an error
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.RB (EINVAL)
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being returned.
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.TP
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.BR MFD_HUGE_2MB ", " MFD_HUGE_1GB ", " "..."
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Used in conjunction with
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.B MFD_HUGETLB
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to select alternative hugetlb page sizes (respectively, 2 MB, 1 GB, ...)
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on systems that support multiple hugetlb page sizes. Definitions for known
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huge page sizes are included in the header file
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.I <sys/memfd.h>.
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For details on encoding huge page sizes not included in the header file,
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see the discussion of the similarly named constants in
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.BR mmap (2).
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.PP
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.PP
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Unused bits in
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Unused bits in
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.I flags
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.I flags
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