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cmake: detect availability of posix_fallocate(3) #5087

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cmake: detect availability of posix_fallocate(3) #5087

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21 changes: 21 additions & 0 deletions src/CMakeLists.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -53,6 +53,27 @@ IF (HAVE_FUTIMENS)
SET(GIT_USE_FUTIMENS 1)
ENDIF ()

CHECK_SYMBOL_EXISTS(posix_fallocate fcntl.h HAVE_POSIX_FALLOCATE)
CHECK_SYMBOL_EXISTS(fallocate fcntl.h HAVE_FALLOCATE)
CHECK_C_SOURCE_COMPILES(
"#include <fcntl.h>
int main(void) { return F_PREALLOCATE; }"
HAVE_F_PREALLOCATE)
CHECK_C_SOURCE_COMPILES(
"#include <fcntl.h>
int main(void) { return F_ALLOCSP64; }"
HAVE_F_ALLOCSP64)
IF(HAVE_F_PREALLOCATE)
# APPLE OR FREEBSD OR NETBSD
SET(GIT_USE_FALLOCATE_BSD 1)
ELSEIF(HAVE_F_ALLOCSP64)
SET(GIT_USE_FALLOCATE_SOLARIS 1)
ELSEIF(HAVE_FALLOCATE)
SET(GIT_USE_FALLOCATE 1)
ELSEIF (HAVE_POSIX_FALLOCATE)
SET(GIT_USE_FALLOCATE_POSIX 1)
ENDIF ()

CHECK_PROTOTYPE_DEFINITION(qsort_r
"void qsort_r(void *base, size_t nmemb, size_t size, void *thunk, int (*compar)(void *, const void *, const void *))"
"" "stdlib.h" HAVE_QSORT_R_BSD)
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4 changes: 4 additions & 0 deletions src/features.h.in
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Expand Up @@ -15,6 +15,10 @@
#cmakedefine GIT_USE_STAT_MTIMESPEC 1
#cmakedefine GIT_USE_STAT_MTIME_NSEC 1
#cmakedefine GIT_USE_FUTIMENS 1
#cmakedefine GIT_USE_FALLOCATE 1
#cmakedefine GIT_USE_FALLOCATE_BSD 1
#cmakedefine GIT_USE_FALLOCATE_POSIX 1
#cmakedefine GIT_USE_FALLOCATE_SOLARIS 1

#cmakedefine GIT_REGEX_REGCOMP_L
#cmakedefine GIT_REGEX_REGCOMP
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62 changes: 54 additions & 8 deletions src/posix.c
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Expand Up @@ -157,14 +157,30 @@ int p_rename(const char *from, const char *to)

int p_fallocate(int fd, off_t offset, off_t len)
{
#if defined (__APPLE__) || (defined (__NetBSD__) && __NetBSD_Version__ < 700000000)
int error = 0, cur;
char buf[BUFSIZ];
off_t pos = 0;

#if defined(GIT_USE_FALLOCATE_POSIX)
if ((error = posix_fallocate(fd, offset, len)) < 0)
if (errno == ENOTSUP)
goto fallback;
#elif defined(GIT_USE_FALLOCATE_SOLARIS)
struct flock64 fl;

fl.l_whence = SEEK_SET;
fl.l_start = offset;
fl.l_len = len;

if ((error = fcntl(fd, F_ALLOCSP64, &fl)) < 0)
goto fallback;
#elif defined(GIT_USE_FALLOCATE_BSD)
fstore_t prealloc;
struct stat st;
size_t newsize;
int error;

if ((error = p_fstat(fd, &st)) < 0)
return error;
return -1;

if (git__add_sizet_overflow(&newsize, offset, len)) {
errno = EINVAL;
Expand All @@ -182,15 +198,45 @@ int p_fallocate(int fd, off_t offset, off_t len)

/*
* fcntl will often error when the file already exists; ignore
* this error since ftruncate will also resize the file (although
* this error since our fallback will also resize the file (although
* likely slower).
*/
fcntl(fd, F_PREALLOCATE, &prealloc);

return ftruncate(fd, (offset + len));
if ((error = fcntl(fd, F_PREALLOCATE, &prealloc)) < 0)
goto fallback;
#elif defined(GIT_USE_FALLOCATE)
do {
error = fallocate(fd, 0, offset, len);
} while (error < 0 && errno == EINTR);
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Can fallocate set EAGAIN?

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That's copy-pasted from #5087 (comment), actually. And isn't EAGAIN usually async network stuff ? I'm scared now…

if (error < 0 && errno == ENOTSUP)
goto fallback;
#else
return posix_fallocate(fd, offset, len);
goto fallback;
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I'd just remove the else block, but that's a matter of taste

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It's protecting against an "unused label" warning on macOS case, actually.

#endif

fallback:
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I don't quite get it. Aren't we now always executing the fallback, regardless of whether the platform-specific implementation succeeded or not?

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Heh, true, I seem to have forgot a few returns when whatever platform-specific version succeeded. IOW, only failures of the (potential) platform fallocate would cause the fallback to run.

/* save offset, seek, write zeroes, restore */
if ((error = p_lseek(fd, 0, SEEK_CUR)) < 0)
return -1;

cur = error;

memset(&buf, '\0', sizeof(buf));

if ((error = p_lseek(fd, offset, SEEK_SET)) < 0)
goto cleanup;

while (pos < len) {
size_t wlen = MIN(len - pos, (off_t)sizeof(buf));
if ((error = p_write(fd, buf, wlen)) < 0)
goto cleanup;
pos += wlen;
}

cleanup:
if ((error = p_lseek(fd, cur, SEEK_SET)) < 0)
return error;

return error;
}

#endif /* GIT_WIN32 */
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2 changes: 2 additions & 0 deletions tests/core/posix.c
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Expand Up @@ -302,5 +302,7 @@ void test_core_posix__fallocate(void)
cl_must_pass(p_lseek(fd, 42, SEEK_SET));
cl_must_pass(p_fallocate(fd, 0, 200));
cl_assert_equal_i(42, p_lseek(fd, 0, SEEK_CUR));
cl_must_pass(p_fallocate(fd, 190, 128));
cl_assert_equal_i(42, p_lseek(fd, 0, SEEK_CUR));
p_close(fd);
}