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posixshm: implement posix_fallocate(2)

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Linux expects to be able to use posix_fallocate(2) on a memfd. Other places
would use this with shm_open(2) to act as a smarter ftruncate(2).

Test has been added to go along with this.

Reviewed by:	kib (earlier version)
Differential Revision:	https://reviews.freebsd.org/D23042
This commit is contained in:
Kyle Evans 2020-01-08 19:08:44 +00:00
parent 7ce4072267
commit f10405323a
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=356512
2 changed files with 67 additions and 0 deletions
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28
sys/kern/uipc_shm.c
View File

@ -138,6 +138,7 @@ static fo_fill_kinfo_t shm_fill_kinfo;
static fo_mmap_t shm_mmap;
static fo_get_seals_t shm_get_seals;
static fo_add_seals_t shm_add_seals;
static fo_fallocate_t shm_fallocate;
/* File descriptor operations. */
struct fileops shm_ops = {
@ -157,6 +158,7 @@ struct fileops shm_ops = {
.fo_mmap = shm_mmap,
.fo_get_seals = shm_get_seals,
.fo_add_seals = shm_add_seals,
.fo_fallocate = shm_fallocate,
.fo_flags = DFLAG_PASSABLE | DFLAG_SEEKABLE
};
@ -1437,6 +1439,32 @@ shm_get_seals(struct file *fp, int *seals)
return (0);
}
static int
shm_fallocate(struct file *fp, off_t offset, off_t len, struct thread *td)
{
void *rl_cookie;
struct shmfd *shmfd;
size_t size;
int error;
/* This assumes that the caller already checked for overflow. */
error = 0;
shmfd = fp->f_data;
size = offset + len;
rl_cookie = rangelock_wlock(&shmfd->shm_rl, 0, OFF_MAX,
&shmfd->shm_mtx);
if (size > shmfd->shm_size) {
VM_OBJECT_WLOCK(shmfd->shm_object);
error = shm_dotruncate_locked(shmfd, size, rl_cookie);
VM_OBJECT_WUNLOCK(shmfd->shm_object);
}
rangelock_unlock(&shmfd->shm_rl, rl_cookie, &shmfd->shm_mtx);
/* Translate to posix_fallocate(2) return value as needed. */
if (error == ENOMEM)
error = ENOSPC;
return (error);
}
static int
sysctl_posix_shm_list(SYSCTL_HANDLER_ARGS)
{

39
tests/sys/posixshm/posixshm_test.c
View File

@ -918,6 +918,44 @@ ATF_TC_BODY(mode, tc)
umask(restore_mask);
}
ATF_TC_WITHOUT_HEAD(fallocate);
ATF_TC_BODY(fallocate, tc)
{
struct stat st;
int error, fd, sz;
/*
* Primitive test case for posix_fallocate with shmd. Effectively
* expected to work like a smarter ftruncate that will grow the region
* as needed in a race-free way.
*/
fd = shm_open(SHM_ANON, O_RDWR, 0666);
ATF_REQUIRE_MSG(fd >= 0, "shm_open failed; errno=%d", errno);
/* Set the initial size. */
sz = 32;
ATF_REQUIRE(ftruncate(fd, sz) == 0);
/* Now grow it. */
error = 0;
sz *= 2;
ATF_REQUIRE_MSG((error = posix_fallocate(fd, 0, sz)) == 0,
"posix_fallocate failed; error=%d", error);
ATF_REQUIRE(fstat(fd, &st) == 0);
ATF_REQUIRE(st.st_size == sz);
/* Attempt to shrink it; should succeed, but not change the size. */
ATF_REQUIRE_MSG((error = posix_fallocate(fd, 0, sz / 2)) == 0,
"posix_fallocate failed; error=%d", error);
ATF_REQUIRE(fstat(fd, &st) == 0);
ATF_REQUIRE(st.st_size == sz);
/* Grow it using an offset of sz and len of sz. */
ATF_REQUIRE_MSG((error = posix_fallocate(fd, sz, sz)) == 0,
"posix_fallocate failed; error=%d", error);
ATF_REQUIRE(fstat(fd, &st) == 0);
ATF_REQUIRE(st.st_size == (sz * 2));
close(fd);
}
ATF_TP_ADD_TCS(tp)
{
@ -951,6 +989,7 @@ ATF_TP_ADD_TCS(tp)
ATF_TP_ADD_TC(tp, object_resize);
ATF_TP_ADD_TC(tp, cloexec);
ATF_TP_ADD_TC(tp, mode);
ATF_TP_ADD_TC(tp, fallocate);
return (atf_no_error());
}