mirror of https://github.com/mkerrisk/man-pages
userfaultfd.2: Add UFFD_FEATURE_THREAD_ID docs
UFFD_FEATURE_THREAD_ID is supported since Linux 4.14. Acked-by: Mike Rapoport <rppt@linux.vnet.ibm.com> Signed-off-by: Peter Xu <peterx@redhat.com> [alx: srcfix] Signed-off-by: Alejandro Colomar <alx.manpages@gmail.com> Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
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@ -77,6 +77,13 @@ When the last file descriptor referring to a userfaultfd object is closed,
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all memory ranges that were registered with the object are unregistered
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and unread events are flushed.
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.\"
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.PP
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Since Linux 4.14, userfaultfd page fault message can selectively embed
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faulting thread ID information into the fault message.
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One needs to enable this feature explicitly using the
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.B UFFD_FEATURE_THREAD_ID
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feature bit when initializing the userfaultfd context.
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By default, thread ID reporting is disabled.
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.SS Usage
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The userfaultfd mechanism is designed to allow a thread in a multithreaded
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program to perform user-space paging for the other threads in the process.
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@ -229,6 +236,9 @@ struct uffd_msg {
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struct {
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__u64 flags; /* Flags describing fault */
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__u64 address; /* Faulting address */
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union {
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__u32 ptid; /* Thread ID of the fault */
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} feat;
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} pagefault;
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struct { /* Since Linux 4.11 */
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@ -358,6 +368,9 @@ otherwise it is a read fault.
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.\" UFFD_PAGEFAULT_FLAG_WP is not yet supported.
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.RE
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.TP
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.I pagefault.feat.pid
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The thread ID that triggered the page fault.
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.TP
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.I fork.ufd
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The file descriptor associated with the userfault object
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created for the child created by
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