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memfd: split qemu_memfd_alloc()

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Add a function to only create a memfd, without mmap. The function is
used in the following memory backend.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20171023141815.17709-2-marcandre.lureau@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
This commit is contained in:
Marc-André Lureau 2017-10-23 15:18:07 +01:00 committed by Eduardo Habkost
parent 3e5bdc6573
commit dcff1035df
2 changed files with 37 additions and 25 deletions
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1
include/qemu/memfd.h
View File

@ -16,6 +16,7 @@
#define F_SEAL_WRITE 0x0008 /* prevent writes */
#endif
int qemu_memfd_create(const char *name, size_t size, unsigned int seals);
void *qemu_memfd_alloc(const char *name, size_t size, unsigned int seals,
int *fd);
void qemu_memfd_free(void *ptr, size_t size, int fd);

61
util/memfd.c
View File

@ -53,6 +53,38 @@ static int memfd_create(const char *name, unsigned int flags)
#define MFD_ALLOW_SEALING 0x0002U
#endif
int qemu_memfd_create(const char *name, size_t size, unsigned int seals)
{
int mfd = -1;
#ifdef CONFIG_LINUX
unsigned int flags = MFD_CLOEXEC;
if (seals) {
flags |= MFD_ALLOW_SEALING;
}
mfd = memfd_create(name, flags);
if (mfd < 0) {
return -1;
}
if (ftruncate(mfd, size) == -1) {
perror("ftruncate");
close(mfd);
return -1;
}
if (seals && fcntl(mfd, F_ADD_SEALS, seals) == -1) {
perror("fcntl");
close(mfd);
return -1;
}
#endif
return mfd;
}
/*
* This is a best-effort helper for shared memory allocation, with
* optional sealing. The helper will do his best to allocate using
@ -63,35 +95,14 @@ void *qemu_memfd_alloc(const char *name, size_t size, unsigned int seals,
int *fd)
{
void *ptr;
int mfd = -1;
int mfd = qemu_memfd_create(name, size, seals);
*fd = -1;
#ifdef CONFIG_LINUX
if (seals) {
mfd = memfd_create(name, MFD_ALLOW_SEALING | MFD_CLOEXEC);
/* some systems have memfd without sealing */
if (mfd == -1) {
mfd = qemu_memfd_create(name, size, 0);
}
if (mfd == -1) {
/* some systems have memfd without sealing */
mfd = memfd_create(name, MFD_CLOEXEC);
seals = 0;
}
#endif
if (mfd != -1) {
if (ftruncate(mfd, size) == -1) {
perror("ftruncate");
close(mfd);
return NULL;
}
if (seals && fcntl(mfd, F_ADD_SEALS, seals) == -1) {
perror("fcntl");
close(mfd);
return NULL;
}
} else {
const char *tmpdir = g_get_tmp_dir();
gchar *fname;