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Provide lstat() for Windows.

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Junction points will be reported with S_ISLNK(x.st_mode), simulating
POSIX lstat().  stat() will follow pseudo-symlinks, like in POSIX (but
only one level before giving up, unlike in POSIX).

This completes a TODO left by commit bed90759fc.

Tested-by: Andrew Dunstan <andrew@dunslane.net> (earlier version)
Discussion: https://postgr.es/m/CA%2BhUKGLfOOeyZpm5ByVcAt7x5Pn-%3DxGRNCvgiUPVVzjFLtnY0w%40mail.gmail.com
This commit is contained in:
Thomas Munro 2022-08-06 12:00:57 +12:00
parent feb593506b
commit c5cb8f3b77
2 changed files with 123 additions and 5 deletions
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18
src/include/port/win32_port.h
View File

@ -278,10 +278,11 @@ struct stat /* This should match struct __stat64 */
extern int _pgfstat64(int fileno, struct stat *buf);
extern int _pgstat64(const char *name, struct stat *buf);
extern int _pglstat64(const char *name, struct stat *buf);
#define fstat(fileno, sb) _pgfstat64(fileno, sb)
#define stat(path, sb) _pgstat64(path, sb)
#define lstat(path, sb) _pgstat64(path, sb)
#define lstat(path, sb) _pglstat64(path, sb)
/* These macros are not provided by older MinGW, nor by MSVC */
#ifndef S_IRUSR
@ -327,6 +328,21 @@ extern int _pgstat64(const char *name, struct stat *buf);
#define S_ISREG(m) (((m) & S_IFMT) == S_IFREG)
#endif
/*
* In order for lstat() to be able to report junction points as symlinks, we
* need to hijack a bit in st_mode, since neither MSVC nor MinGW provides
* S_ISLNK and there aren't any spare bits. We'll steal the one for character
* devices, because we don't otherwise make use of those.
*/
#ifdef S_ISLNK
#error "S_ISLNK is already defined"
#endif
#ifdef S_IFLNK
#error "S_IFLNK is already defined"
#endif
#define S_IFLNK S_IFCHR
#define S_ISLNK(m) (((m) & S_IFLNK) == S_IFLNK)
/*
* Supplement to <fcntl.h>.
* This is the same value as _O_NOINHERIT in the MS header file. This is

110
src/port/win32stat.c
View File

@ -15,7 +15,11 @@
#ifdef WIN32
#define UMDF_USING_NTSTATUS
#include "c.h"
#include "port/win32ntdll.h"
#include <windows.h>
/*
@ -107,12 +111,10 @@ fileinfo_to_stat(HANDLE hFile, struct stat *buf)
}
/*
* Windows implementation of stat().
*
* This currently also implements lstat(), though perhaps that should change.
* Windows implementation of lstat().
*/
int
_pgstat64(const char *name, struct stat *buf)
_pglstat64(const char *name, struct stat *buf)
{
/*
* Our open wrapper will report STATUS_DELETE_PENDING as ENOENT. We
@ -129,10 +131,110 @@ _pgstat64(const char *name, struct stat *buf)
ret = fileinfo_to_stat(hFile, buf);
/*
* Junction points appear as directories to fileinfo_to_stat(), so we'll
* need to do a bit more work to distinguish them.
*/
if (ret == 0 && S_ISDIR(buf->st_mode))
{
char next[MAXPGPATH];
ssize_t size;
/*
* POSIX says we need to put the length of the target path into
* st_size. Use readlink() to get it, or learn that this is not a
* junction point.
*/
size = readlink(name, next, sizeof(next));
if (size < 0)
{
if (errno == EACCES &&
pg_RtlGetLastNtStatus() == STATUS_DELETE_PENDING)
{
/* Unlinked underneath us. */
errno = ENOENT;
ret = -1;
}
else if (errno == EINVAL)
{
/* It's not a junction point, nothing to do. */
}
else
{
/* Some other failure. */
ret = -1;
}
}
else
{
/* It's a junction point, so report it as a symlink. */
buf->st_mode &= ~S_IFDIR;
buf->st_mode |= S_IFLNK;
buf->st_size = size;
}
}
CloseHandle(hFile);
return ret;
}
/*
* Windows implementation of stat().
*/
int
_pgstat64(const char *name, struct stat *buf)
{
int ret;
ret = _pglstat64(name, buf);
/* Do we need to follow a symlink (junction point)? */
if (ret == 0 && S_ISLNK(buf->st_mode))
{
char next[MAXPGPATH];
ssize_t size;
/*
* _pglstat64() already called readlink() once to be able to fill in
* st_size, and now we need to do it again to get the path to follow.
* That could be optimized, but stat() on symlinks is probably rare
* and this way is simple.
*/
size = readlink(name, next, sizeof(next));
if (size < 0)
{
if (errno == EACCES &&
pg_RtlGetLastNtStatus() == STATUS_DELETE_PENDING)
{
/* Unlinked underneath us. */
errno = ENOENT;
}
return -1;
}
if (size >= sizeof(next))
{
errno = ENAMETOOLONG;
return -1;
}
next[size] = 0;
ret = _pglstat64(next, buf);
if (ret == 0 && S_ISLNK(buf->st_mode))
{
/*
* We're only prepared to go one hop, because we only expect to
* deal with the simple cases that we create. The error for too
* many symlinks is supposed to be ELOOP, but Windows hasn't got
* it.
*/
errno = EIO;
return -1;
}
}
return ret;
}
/*
* Windows implementation of fstat().
*/