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util: add linux-only memfd fallback

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Implement memfd_create() fallback if not available in system libc.
memfd_create() is still not included in glibc today, atlhough it's been
available since Linux 3.17 in Oct 2014.

memfd has numerous advantages over traditional shm/mmap for ipc memory
sharing with fd handler, which we are going to make use of for
vhost-user logging memory in following patches.

The next patches are going to introduce helpers to use best practices of
memfd usage and provide some compatibility fallback. memfd.c is thus
temporarily useless and eventually empty if memfd_create() is provided
by the system.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Tested-by: Thibaut Collet <thibaut.collet@6wind.com>
This commit is contained in:
Marc-André Lureau 2015-10-09 17:17:19 +02:00 • committed by Michael S. Tsirkin
parent e279200458
commit f04cf9239a
3 changed files with 75 additions and 0 deletions
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20
include/qemu/memfd.h Normal file
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#ifndef QEMU_MEMFD_H
#define QEMU_MEMFD_H
#include "config-host.h"
#ifndef F_LINUX_SPECIFIC_BASE
#define F_LINUX_SPECIFIC_BASE 1024
#endif
#ifndef F_ADD_SEALS
#define F_ADD_SEALS (F_LINUX_SPECIFIC_BASE + 9)
#define F_GET_SEALS (F_LINUX_SPECIFIC_BASE + 10)
#define F_SEAL_SEAL 0x0001 /* prevent further seals from being set */
#define F_SEAL_SHRINK 0x0002 /* prevent file from shrinking */
#define F_SEAL_GROW 0x0004 /* prevent file from growing */
#define F_SEAL_WRITE 0x0008 /* prevent writes */
#endif
#endif /* QEMU_MEMFD_H */