dirmod.c

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/*-------------------------------------------------------------------------
 *
 * dirmod.c
 *    directory handling functions
 *
 * Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *  This includes replacement versions of functions that work on
 *  Windows.
 *
 * IDENTIFICATION
 *    src/port/dirmod.c
 *
 *-------------------------------------------------------------------------
 */
 
#ifndef FRONTEND
#include "postgres.h"
#else
#include "postgres_fe.h"
#endif
 
/* Don't modify declarations in system headers */
#if defined(WIN32) || defined(__CYGWIN__)
#undef rename
#undef unlink
#endif
 
#include <unistd.h>
#include <sys/stat.h>
 
#if defined(WIN32) || defined(__CYGWIN__)
#ifndef __CYGWIN__
#include <winioctl.h>
#else
#include <windows.h>
#include <w32api/winioctl.h>
#endif
#endif
 
#if defined(WIN32) && !defined(__CYGWIN__)
#include "port/win32ntdll.h"
#endif
 
#if defined(WIN32) || defined(__CYGWIN__)
 
/*
 *  pgrename
 */
int
pgrename(const char *from, const char *to)
{
    int         loops = 0;
 
    /*
     * We need to loop because even though PostgreSQL uses flags that allow
     * rename while the file is open, other applications might have the file
     * open without those flags.  However, we won't wait indefinitely for
     * someone else to close the file, as the caller might be holding locks
     * and blocking other backends.
     */
#if defined(WIN32) && !defined(__CYGWIN__)
    while (!MoveFileEx(from, to, MOVEFILE_REPLACE_EXISTING))
#else
    while (rename(from, to) < 0)
#endif
    {
#if defined(WIN32) && !defined(__CYGWIN__)
        DWORD       err = GetLastError();
 
        _dosmaperr(err);
 
        /*
         * Modern NT-based Windows versions return ERROR_SHARING_VIOLATION if
         * another process has the file open without FILE_SHARE_DELETE.
         * ERROR_LOCK_VIOLATION has also been seen with some anti-virus
         * software. This used to check for just ERROR_ACCESS_DENIED, so
         * presumably you can get that too with some OS versions. We don't
         * expect real permission errors where we currently use rename().
         */
        if (err != ERROR_ACCESS_DENIED &&
            err != ERROR_SHARING_VIOLATION &&
            err != ERROR_LOCK_VIOLATION)
            return -1;
#else
        if (errno != EACCES)
            return -1;
#endif
 
        if (++loops > 100)      /* time out after 10 sec */
            return -1;
        pg_usleep(100000);      /* us */
    }
    return 0;
}
 
/*
 * Check if _pglstat64()'s reason for failure was STATUS_DELETE_PENDING.
 * This doesn't apply to Cygwin, which has its own lstat() that would report
 * the case as EACCES.
*/
static bool
lstat_error_was_status_delete_pending(void)
{
    if (errno != ENOENT)
        return false;
#if defined(WIN32) && !defined(__CYGWIN__)
    if (pg_RtlGetLastNtStatus() == STATUS_DELETE_PENDING)
        return true;
#endif
    return false;
}
 
/*
 *  pgunlink
 */
int
pgunlink(const char *path)
{
    bool        is_lnk;
    int         loops = 0;
    struct stat st;
 
    /*
     * This function might be called for a regular file or for a junction
     * point (which we use to emulate symlinks).  The latter must be unlinked
     * with rmdir() on Windows.  Before we worry about any of that, let's see
     * if we can unlink directly, since that's expected to be the most common
     * case.
     */
    if (unlink(path) == 0)
        return 0;
    if (errno != EACCES)
        return -1;
 
    /*
     * EACCES is reported for many reasons including unlink() of a junction
     * point.  Check if that's the case so we can redirect to rmdir().
     *
     * Note that by checking only once, we can't cope with a path that changes
     * from regular file to junction point underneath us while we're retrying
     * due to sharing violations, but that seems unlikely.  We could perhaps
     * prevent that by holding a file handle ourselves across the lstat() and
     * the retry loop, but that seems like over-engineering for now.
     *
     * In the special case of a STATUS_DELETE_PENDING error (file already
     * unlinked, but someone still has it open), we don't want to report
     * ENOENT to the caller immediately, because rmdir(parent) would probably
     * fail. We want to wait until the file truly goes away so that simple
     * recursive directory unlink algorithms work.
     */
    if (lstat(path, &st) < 0)
    {
        if (lstat_error_was_status_delete_pending())
            is_lnk = false;
        else
            return -1;
    }
    else
        is_lnk = S_ISLNK(st.st_mode);
 
    /*
     * We need to loop because even though PostgreSQL uses flags that allow
     * unlink while the file is open, other applications might have the file
     * open without those flags.  However, we won't wait indefinitely for
     * someone else to close the file, as the caller might be holding locks
     * and blocking other backends.
     */
    while ((is_lnk ? rmdir(path) : unlink(path)) < 0)
    {
        if (errno != EACCES)
            return -1;
        if (++loops > 100)      /* time out after 10 sec */
            return -1;
        pg_usleep(100000);      /* us */
    }
    return 0;
}
 
/* We undefined these above; now redefine for possible use below */
#define rename(from, to)        pgrename(from, to)
#define unlink(path)            pgunlink(path)
#endif                          /* defined(WIN32) || defined(__CYGWIN__) */
 
 
#if defined(WIN32) && !defined(__CYGWIN__)  /* Cygwin has its own symlinks */
 
/*
 *  pgsymlink support:
 *
 *  This struct is a replacement for REPARSE_DATA_BUFFER which is defined in VC6 winnt.h
 *  but omitted in later SDK functions.
 *  We only need the SymbolicLinkReparseBuffer part of the original struct's union.
 */
typedef struct
{
    DWORD       ReparseTag;
    WORD        ReparseDataLength;
    WORD        Reserved;
    /* SymbolicLinkReparseBuffer */
    WORD        SubstituteNameOffset;
    WORD        SubstituteNameLength;
    WORD        PrintNameOffset;
    WORD        PrintNameLength;
    WCHAR       PathBuffer[FLEXIBLE_ARRAY_MEMBER];
} REPARSE_JUNCTION_DATA_BUFFER;
 
#define REPARSE_JUNCTION_DATA_BUFFER_HEADER_SIZE   \
        FIELD_OFFSET(REPARSE_JUNCTION_DATA_BUFFER, SubstituteNameOffset)
 
 
/*
 *  pgsymlink - uses Win32 junction points
 *
 *  For reference:  http://www.codeproject.com/KB/winsdk/junctionpoints.aspx
 */
int
pgsymlink(const char *oldpath, const char *newpath)
{
    HANDLE      dirhandle;
    DWORD       len;
    char        buffer[MAX_PATH * sizeof(WCHAR) + offsetof(REPARSE_JUNCTION_DATA_BUFFER, PathBuffer)];
    char        nativeTarget[MAX_PATH];
    char       *p = nativeTarget;
    REPARSE_JUNCTION_DATA_BUFFER *reparseBuf = (REPARSE_JUNCTION_DATA_BUFFER *) buffer;
 
    CreateDirectory(newpath, 0);
    dirhandle = CreateFile(newpath, GENERIC_READ | GENERIC_WRITE,
                           0, 0, OPEN_EXISTING,
                           FILE_FLAG_OPEN_REPARSE_POINT | FILE_FLAG_BACKUP_SEMANTICS, 0);
 
    if (dirhandle == INVALID_HANDLE_VALUE)
    {
        _dosmaperr(GetLastError());
        return -1;
    }
 
    /* make sure we have an unparsed native win32 path */
    if (memcmp("\\??\\", oldpath, 4) != 0)
        snprintf(nativeTarget, sizeof(nativeTarget), "\\??\\%s", oldpath);
    else
        strlcpy(nativeTarget, oldpath, sizeof(nativeTarget));
 
    while ((p = strchr(p, '/')) != NULL)
        *p++ = '\\';
 
    len = strlen(nativeTarget) * sizeof(WCHAR);
    reparseBuf->ReparseTag = IO_REPARSE_TAG_MOUNT_POINT;
    reparseBuf->ReparseDataLength = len + 12;
    reparseBuf->Reserved = 0;
    reparseBuf->SubstituteNameOffset = 0;
    reparseBuf->SubstituteNameLength = len;
    reparseBuf->PrintNameOffset = len + sizeof(WCHAR);
    reparseBuf->PrintNameLength = 0;
    MultiByteToWideChar(CP_ACP, 0, nativeTarget, -1,
                        reparseBuf->PathBuffer, MAX_PATH);
 
    /*
     * FSCTL_SET_REPARSE_POINT is coded differently depending on SDK version;
     * we use our own definition
     */
    if (!DeviceIoControl(dirhandle,
                         CTL_CODE(FILE_DEVICE_FILE_SYSTEM, 41, METHOD_BUFFERED, FILE_ANY_ACCESS),
                         reparseBuf,
                         reparseBuf->ReparseDataLength + REPARSE_JUNCTION_DATA_BUFFER_HEADER_SIZE,
                         0, 0, &len, 0))
    {
        LPSTR       msg;
        int         save_errno;
 
        _dosmaperr(GetLastError());
        save_errno = errno;
 
        FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER |
                      FORMAT_MESSAGE_IGNORE_INSERTS |
                      FORMAT_MESSAGE_FROM_SYSTEM,
                      NULL, GetLastError(),
                      MAKELANGID(LANG_ENGLISH, SUBLANG_DEFAULT),
                      (LPSTR) &msg, 0, NULL);
#ifndef FRONTEND
        ereport(ERROR,
                (errcode_for_file_access(),
                 errmsg("could not set junction for \"%s\": %s",
                        nativeTarget, msg)));
#else
        fprintf(stderr, _("could not set junction for \"%s\": %s\n"),
                nativeTarget, msg);
#endif
        LocalFree(msg);
 
        CloseHandle(dirhandle);
        RemoveDirectory(newpath);
 
        errno = save_errno;
 
        return -1;
    }
 
    CloseHandle(dirhandle);
 
    return 0;
}
 
/*
 *  pgreadlink - uses Win32 junction points
 */
int
pgreadlink(const char *path, char *buf, size_t size)
{
    DWORD       attr;
    HANDLE      h;
    char        buffer[MAX_PATH * sizeof(WCHAR) + offsetof(REPARSE_JUNCTION_DATA_BUFFER, PathBuffer)];
    REPARSE_JUNCTION_DATA_BUFFER *reparseBuf = (REPARSE_JUNCTION_DATA_BUFFER *) buffer;
    DWORD       len;
    int         r;
 
    attr = GetFileAttributes(path);
    if (attr == INVALID_FILE_ATTRIBUTES)
    {
        _dosmaperr(GetLastError());
        return -1;
    }
    if ((attr & FILE_ATTRIBUTE_REPARSE_POINT) == 0)
    {
        errno = EINVAL;
        return -1;
    }
 
    h = CreateFile(path,
                   GENERIC_READ,
                   FILE_SHARE_READ | FILE_SHARE_WRITE,
                   NULL,
                   OPEN_EXISTING,
                   FILE_FLAG_OPEN_REPARSE_POINT | FILE_FLAG_BACKUP_SEMANTICS,
                   0);
    if (h == INVALID_HANDLE_VALUE)
    {
        _dosmaperr(GetLastError());
        return -1;
    }
 
    if (!DeviceIoControl(h,
                         FSCTL_GET_REPARSE_POINT,
                         NULL,
                         0,
                         (LPVOID) reparseBuf,
                         sizeof(buffer),
                         &len,
                         NULL))
    {
        LPSTR       msg;
 
        errno = 0;
        FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER |
                      FORMAT_MESSAGE_IGNORE_INSERTS |
                      FORMAT_MESSAGE_FROM_SYSTEM,
                      NULL, GetLastError(),
                      MAKELANGID(LANG_ENGLISH, SUBLANG_DEFAULT),
                      (LPSTR) &msg, 0, NULL);
#ifndef FRONTEND
        ereport(ERROR,
                (errcode_for_file_access(),
                 errmsg("could not get junction for \"%s\": %s",
                        path, msg)));
#else
        fprintf(stderr, _("could not get junction for \"%s\": %s\n"),
                path, msg);
#endif
        LocalFree(msg);
        CloseHandle(h);
        errno = EINVAL;
        return -1;
    }
    CloseHandle(h);
 
    /* Got it, let's get some results from this */
    if (reparseBuf->ReparseTag != IO_REPARSE_TAG_MOUNT_POINT)
    {
        errno = EINVAL;
        return -1;
    }
 
    r = WideCharToMultiByte(CP_ACP, 0,
                            reparseBuf->PathBuffer, -1,
                            buf,
                            size,
                            NULL, NULL);
 
    if (r <= 0)
    {
        errno = EINVAL;
        return -1;
    }
 
    /* r includes the null terminator */
    r -= 1;
 
    /*
     * If the path starts with "\??\" followed by a "drive absolute" path
     * (known to Windows APIs as RtlPathTypeDriveAbsolute), then strip that
     * prefix.  This undoes some of the transformation performed by
     * pgsymlink(), to get back to a format that users are used to seeing.  We
     * don't know how to transform other path types that might be encountered
     * outside PGDATA, so we just return them directly.
     */
    if (r >= 7 &&
        buf[0] == '\\' &&
        buf[1] == '?' &&
        buf[2] == '?' &&
        buf[3] == '\\' &&
        isalpha(buf[4]) &&
        buf[5] == ':' &&
        buf[6] == '\\')
    {
        memmove(buf, buf + 4, strlen(buf + 4) + 1);
        r -= 4;
    }
    return r;
}
 
#endif                          /* defined(WIN32) && !defined(__CYGWIN__) */