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memfd_create.2: Update manpage with new memfd F_SEAL_FUTURE_WRITE seal 

More details of the seal can be found in the LKML patch:
https://lore.kernel.org/lkml/20181120052137.74317-1-joel@joelfernandes.org/T/#t

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Joel Fernandes (Google) 2019-03-14 17:48:44 -04:00 committed by Michael Kerrisk
parent e1cd30eb5e
commit 98eff9f7e5
1 changed files with 14 additions and 1 deletions
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15
man2/memfd_create.2
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@ -280,7 +280,15 @@ in order to restrict further modifications on the file.
(If placing the seal
.BR F_SEAL_WRITE ,
then it will be necessary to first unmap the shared writable mapping
created in the previous step.)
created in the previous step. Otherwise, behavior similar to
.BR F_SEAL_WRITE
can be achieved, by using
.BR F_SEAL_FUTURE_WRITE
which will prevent future writes via
.BR mmap (2)
and
.BR write (2)
from succeeding, while keeping existing shared writable mappings).
.IP 4.
A second process obtains a file descriptor for the
.BR tmpfs (5)
@ -425,6 +433,7 @@ main(int argc, char *argv[])
fprintf(stderr, "\et\etg \- F_SEAL_GROW\en");
fprintf(stderr, "\et\ets \- F_SEAL_SHRINK\en");
fprintf(stderr, "\et\etw \- F_SEAL_WRITE\en");
fprintf(stderr, "\et\etW \- F_SEAL_FUTURE_WRITE\en");
fprintf(stderr, "\et\etS \- F_SEAL_SEAL\en");
exit(EXIT_FAILURE);
}
@ -463,6 +472,8 @@ main(int argc, char *argv[])
seals |= F_SEAL_SHRINK;
if (strchr(seals_arg, \(aqw\(aq) != NULL)
seals |= F_SEAL_WRITE;
if (strchr(seals_arg, \(aqW\(aq) != NULL)
seals |= F_SEAL_FUTURE_WRITE;
if (strchr(seals_arg, \(aqS\(aq) != NULL)
seals |= F_SEAL_SEAL;
@ -518,6 +529,8 @@ main(int argc, char *argv[])
printf(" GROW");
if (seals & F_SEAL_WRITE)
printf(" WRITE");
if (seals & F_SEAL_FUTURE_WRITE)
printf(" FUTURE_WRITE");
if (seals & F_SEAL_SHRINK)
printf(" SHRINK");
printf("\en");