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RE: [PATCH v5 04/16] hw/9pfs: Implement Windows specific xxxdir() APIs
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From: |
Shi, Guohuai |
|
Subject: |
RE: [PATCH v5 04/16] hw/9pfs: Implement Windows specific xxxdir() APIs |
|
Date: |
Thu, 16 Mar 2023 17:28:15 +0000 |
> -----Original Message-----
> From: Christian Schoenebeck <qemu_oss@crudebyte.com>
> Sent: Thursday, March 16, 2023 19:05
> To: Greg Kurz <groug@kaod.org>; qemu-devel@nongnu.org
> Cc: Meng, Bin <Bin.Meng@windriver.com>; Shi, Guohuai
> <Guohuai.Shi@windriver.com>
> Subject: Re: [PATCH v5 04/16] hw/9pfs: Implement Windows specific xxxdir()
> APIs
>
> CAUTION: This email comes from a non Wind River email account!
> Do not click links or open attachments unless you recognize the sender and
> know the content is safe.
>
> On Wednesday, March 15, 2023 8:05:34 PM CET Shi, Guohuai wrote:
> >
> > > -----Original Message-----
> > > From: Christian Schoenebeck <qemu_oss@crudebyte.com>
> > > Sent: Wednesday, March 15, 2023 00:06
> > > To: Greg Kurz <groug@kaod.org>; qemu-devel@nongnu.org
> > > Cc: Shi, Guohuai <Guohuai.Shi@windriver.com>; Meng, Bin
> > > <Bin.Meng@windriver.com>
> > > Subject: Re: [PATCH v5 04/16] hw/9pfs: Implement Windows specific
> > > xxxdir() APIs
> > >
> > > CAUTION: This email comes from a non Wind River email account!
> > > Do not click links or open attachments unless you recognize the
> > > sender and know the content is safe.
> > >
> > > On Monday, February 20, 2023 11:08:03 AM CET Bin Meng wrote:
> > > > From: Guohuai Shi <guohuai.shi@windriver.com>
> > > >
> > > > This commit implements Windows specific xxxdir() APIs for safety
> > > > directory access.
> > >
> > > That comment is seriously too short for this patch.
> > >
> > > 1. You should describe the behaviour implementation that you have
> > > chosen and why you have chosen it.
> > >
> > > 2. Like already said in the previous version of the patch, you
> > > should place a link to the discussion we had on this issue.
> > >
> > > > Signed-off-by: Guohuai Shi <guohuai.shi@windriver.com>
> > > > Signed-off-by: Bin Meng <bin.meng@windriver.com>
> > > > ---
> > > >
> > > > hw/9pfs/9p-util.h | 6 +
> > > > hw/9pfs/9p-util-win32.c | 443
> > > > ++++++++++++++++++++++++++++++++++++++++
> > > > 2 files changed, 449 insertions(+)
> > > >
> > > > diff --git a/hw/9pfs/9p-util.h b/hw/9pfs/9p-util.h index
> > > > 0f159fb4ce..c1c251fbd1 100644
> > > > --- a/hw/9pfs/9p-util.h
> > > > +++ b/hw/9pfs/9p-util.h
> > > > @@ -141,6 +141,12 @@ int unlinkat_win32(int dirfd, const char
> > > > *pathname, int flags); int statfs_win32(const char *root_path,
> > > > struct statfs *stbuf); int openat_dir(int dirfd, const char
> > > > *name); int openat_file(int dirfd, const char *name, int flags,
> > > > mode_t mode);
> > > > +DIR *opendir_win32(const char *full_file_name); int
> > > > +closedir_win32(DIR *pDir); struct dirent *readdir_win32(DIR
> > > > +*pDir); void rewinddir_win32(DIR *pDir); void seekdir_win32(DIR
> > > > +*pDir, long pos); long telldir_win32(DIR *pDir);
> > > > #endif
> > > >
> > > > static inline void close_preserve_errno(int fd) diff --git
> > > > a/hw/9pfs/9p-util-win32.c b/hw/9pfs/9p-util-win32.c index
> > > > a99d579a06..e9408f3c45 100644
> > > > --- a/hw/9pfs/9p-util-win32.c
> > > > +++ b/hw/9pfs/9p-util-win32.c
> > > > @@ -37,6 +37,16 @@
> > > > * Windows does not support opendir, the directory fd is created by
> > > > * CreateFile and convert to fd by _open_osfhandle(). Keep the fd
> open
> > > will
> > > > * lock and protect the directory (can not be modified or replaced)
> > > > + *
> > > > + * 5. Neither Windows native APIs, nor MinGW provide a POSIX
> > > > + compatible
> > > API for
> > > > + * acquiring directory entries in a safe way. Calling those APIs
> > > (native
> > > > + * _findfirst() and _findnext() or MinGW's readdir(), seekdir() and
> > > > + * telldir()) directly can lead to an inconsistent state if
> directory
> > > is
> > > > + * modified in between, e.g. the same directory appearing more than
> > > once
> > > > + * in output, or directories not appearing at all in output even
> though
> > > they
> > > > + * were neither newly created nor deleted. POSIX does not define
> what
> > > happens
> > > > + * with deleted or newly created directories in between, but it
> > > guarantees a
> > > > + * consistent state.
> > > > */
> > > >
> > > > #include "qemu/osdep.h"
> > > > @@ -51,6 +61,25 @@
> > > >
> > > > #define V9FS_MAGIC 0x53465039 /* string "9PFS" */
> > > >
> > > > +/*
> > > > + * MinGW and Windows does not provide a safe way to seek
> > > > +directory while other
> > > > + * thread is modifying the same directory.
> > > > + *
> > > > + * This structure is used to store sorted file id and ensure
> > > > +directory seek
> > > > + * consistency.
> > > > + */
> > > > +struct dir_win32 {
> > > > + struct dirent dd_dir;
> > > > + uint32_t offset;
> > > > + uint32_t total_entries;
> > > > + HANDLE hDir;
> > > > + uint32_t dir_name_len;
> > > > + uint64_t dot_id;
> > > > + uint64_t dot_dot_id;
> > > > + uint64_t *file_id_list;
> > > > + char dd_name[1];
> > > > +};
> > > > +
> > > > /*
> > > > * win32_error_to_posix - convert Win32 error to POSIX error number
> > > > *
> > > > @@ -977,3 +1006,417 @@ int qemu_mknodat(int dirfd, const char
> > > > *filename,
> > > mode_t mode, dev_t dev)
> > > > errno = ENOTSUP;
> > > > return -1;
> > > > }
> > > > +
> > > > +static int file_id_compare(const void *id_ptr1, const void
> > > > +*id_ptr2) {
> > > > + uint64_t id[2];
> > > > +
> > > > + id[0] = *(uint64_t *)id_ptr1;
> > > > + id[1] = *(uint64_t *)id_ptr2;
> > > > +
> > > > + if (id[0] > id[1]) {
> > > > + return 1;
> > > > + } else if (id[0] < id[1]) {
> > > > + return -1;
> > > > + } else {
> > > > + return 0;
> > > > + }
> > > > +}
> > > > +
> > > > +static int get_next_entry(struct dir_win32 *stream) {
> > > > + HANDLE hDirEntry = INVALID_HANDLE_VALUE;
> > > > + char *entry_name;
> > > > + char *entry_start;
> > > > + FILE_ID_DESCRIPTOR fid;
> > > > + DWORD attribute;
> > > > +
> > > > + if (stream->file_id_list[stream->offset] == stream->dot_id) {
> > > > + strcpy(stream->dd_dir.d_name, ".");
> > > > + return 0;
> > > > + }
> > > > +
> > > > + if (stream->file_id_list[stream->offset] == stream->dot_dot_id) {
> > > > + strcpy(stream->dd_dir.d_name, "..");
> > > > + return 0;
> > > > + }
> > > > +
> > > > + fid.dwSize = sizeof(fid);
> > > > + fid.Type = FileIdType;
> > > > +
> > > > + fid.FileId.QuadPart = stream->file_id_list[stream->offset];
> > > > +
> > > > + hDirEntry = OpenFileById(stream->hDir, &fid, GENERIC_READ,
> > > > + FILE_SHARE_READ | FILE_SHARE_WRITE
> > > > + | FILE_SHARE_DELETE,
> > > > + NULL,
> > > > + FILE_FLAG_BACKUP_SEMANTICS
> > > > + | FILE_FLAG_OPEN_REPARSE_POINT);
> > >
> > > What's the purpose of FILE_FLAG_OPEN_REPARSE_POINT here? As it's
> > > apparently not obvious, please add a comment.
> > >
> >
> > If do not use this flag, and if file id is a symbolic link, then Windows
> will not symbolic link itself, but open the target file.
> > This flag is similar as O_NOFOLLOW flag.
>
> OK, got it, thanks! But please add a comment in code that describes this.
>
> > > > +
> > > > + if (hDirEntry == INVALID_HANDLE_VALUE) {
> > > > + /*
> > > > + * Not open it successfully, it may be deleted.
> > >
> > > Wrong English. "Open failed, it may have been deleted in the meantime.".
> > >
> > > > + * Try next id.
> > > > + */
> > > > + return -1;
> > > > + }
> > > > +
> > > > + entry_name = get_full_path_win32(hDirEntry, NULL);
> > > > +
> > > > + CloseHandle(hDirEntry);
> > > > +
> > > > + if (entry_name == NULL) {
> > > > + return -1;
> > > > + }
> > > > +
> > > > + attribute = GetFileAttributes(entry_name);
> > > > +
> > > > + /* symlink is not allowed */
> > > > + if (attribute == INVALID_FILE_ATTRIBUTES
> > > > + || (attribute & FILE_ATTRIBUTE_REPARSE_POINT) != 0) {
> > > > + return -1;
> > >
> > > Wouldn't it make sense to call warn_report_once() here to let the
> > > user know that he has some symlinks that are never delivered to guest?
> >
> > OK, Got it.
> >
> > >
> > > > + }
> > > > +
> > > > + if (memcmp(entry_name, stream->dd_name, stream->dir_name_len)
> > > > + !=
> > > > + 0) {
> > >
> > > No, that's unsafe. You want to use something like strncmp() instead.
> > >
> > > > + /*
> > > > + * The full entry file name should be a part of parent
> > > > + directory
> > > name,
> > > > + * except dot and dot_dot (is already handled).
> > > > + * If not, this entry should not be returned.
> > > > + */
> > > > + return -1;
> > > > + }
> > > > +
> > > > + entry_start = entry_name + stream->dir_name_len;
> > >
> > > s/entry_start/entry_basename/ ?
> > >
> > > > +
> > > > + /* skip slash */
> > > > + while (*entry_start == '\\') {
> > > > + entry_start++;
> > > > + }
> > > > +
> > > > + if (strchr(entry_start, '\\') != NULL) {
> > > > + return -1;
> > > > + }
> > > > +
> > > > + if (strlen(entry_start) == 0
> > > > + || strlen(entry_start) + 1 > sizeof(stream->dd_dir.d_name)) {
> > > > + return -1;
> > > > + }
> > > > + strcpy(stream->dd_dir.d_name, entry_start);
> > >
> > > g_path_get_basename() ? :)
> >
> > For above three comments:
> > This code is not good, should be fixed.
> > The code want to filter the following cases:
> > The parent directory path is not a part of entry's full path:
> > Parent: C:\123\456, entry: C:\123, C:\ Entry contains more than one
> > name components:
> > Parent: C:\123\456, entry: C:\123\456\789\abc Entry is zero length or
> > name buffer is too long
> >
> > I will refactor this part.
>
> In general: writing parsing code yourself is extremely error prone. That's
> why it makes sense to use existing functions from glib, etc.
>
> > >
> > > > +
> > > > + return 0;
> > > > +}
> > > > +
> > > > +/*
> > > > + * opendir_win32 - open a directory
> > > > + *
> > > > + * This function opens a directory and caches all directory entries.
> > >
> > > It just caches all file IDs, doesn't it?
> > >
> >
> > Will fix it
> >
> > > > + */
> > > > +DIR *opendir_win32(const char *full_file_name) {
> > > > + HANDLE hDir = INVALID_HANDLE_VALUE;
> > > > + HANDLE hDirEntry = INVALID_HANDLE_VALUE;
> > > > + char *full_dir_entry = NULL;
> > > > + DWORD attribute;
> > > > + intptr_t dd_handle = -1;
> > > > + struct _finddata_t dd_data;
> > > > + uint64_t file_id;
> > > > + uint64_t *file_id_list = NULL;
> > > > + BY_HANDLE_FILE_INFORMATION FileInfo;
> > >
> > > FileInfo is the variable name, not a struct name, so no upper case
> > > for it please.
> >
> > Will fix it.
> > >
> > > > + struct dir_win32 *stream = NULL;
> > > > + int err = 0;
> > > > + int find_status;
> > > > + int sort_first_two_entry = 0;
> > > > + uint32_t list_count = 16;
> > >
> > > Magic number 16?
> >
> > Will change it to a macro.
> > >
> > > > + uint32_t index = 0;
> > > > +
> > > > + /* open directory to prevent it being removed */
> > > > +
> > > > + hDir = CreateFile(full_file_name, GENERIC_READ,
> > > > + FILE_SHARE_READ | FILE_SHARE_WRITE |
> > > FILE_SHARE_DELETE,
> > > > + NULL,
> > > > + OPEN_EXISTING,
> > > > + FILE_FLAG_BACKUP_SEMANTICS |
> > > FILE_FLAG_OPEN_REPARSE_POINT,
> > > > + NULL);
> > > > +
> > > > + if (hDir == INVALID_HANDLE_VALUE) {
> > > > + err = win32_error_to_posix(GetLastError());
> > > > + goto out;
> > > > + }
> > > > +
> > > > + attribute = GetFileAttributes(full_file_name);
> > > > +
> > > > + /* symlink is not allow */
> > > > + if (attribute == INVALID_FILE_ATTRIBUTES
> > > > + || (attribute & FILE_ATTRIBUTE_REPARSE_POINT) != 0) {
> > > > + err = EACCES;
> > > > + goto out;
> > > > + }
> > > > +
> > > > + /* check if it is a directory */
> > > > + if ((attribute & FILE_ATTRIBUTE_DIRECTORY) == 0) {
> > > > + err = ENOTDIR;
> > > > + goto out;
> > > > + }
> > > > +
> > > > + file_id_list = g_malloc0(sizeof(uint64_t) * list_count);
> > > > +
> > > > + /*
> > > > + * findfirst() needs suffix format name like "\dir1\dir2\*",
> > > > + * allocate more buffer to store suffix.
> > > > + */
> > > > + stream = g_malloc0(sizeof(struct dir_win32) +
> > > > + strlen(full_file_name) + 3);
> > >
> > > Not that I would care much, but +2 would be correct here, as you
> > > declared the struct with one character already, so it is not a
> > > classic (zero size) flex
> > > array:
> > >
> > > struct dir_win32 {
> > > ...
> > > char dd_name[1];
> > > };
> > >
> > Will fix it.
> >
> > > > +
> > > > + strcpy(stream->dd_name, full_file_name);
> > > > + strcat(stream->dd_name, "\\*");
> > > > +
> > > > + stream->hDir = hDir;
> > > > + stream->dir_name_len = strlen(full_file_name);
> > > > +
> > > > + dd_handle = _findfirst(stream->dd_name, &dd_data);
> > > > +
> > > > + if (dd_handle == -1) {
> > > > + err = errno;
> > > > + goto out;
> > > > + }
> > > > +
> > > > + /* read all entries to link list */
> > >
> > > "read all entries as a linked list"
> > >
> > > However there is no linked list here. It seems to be an array.
> >
> > Will fix it.
> > >
> > > > + do {
> > > > + full_dir_entry = get_full_path_win32(hDir, dd_data.name);
> > > > +
> > > > + if (full_dir_entry == NULL) {
> > > > + err = ENOMEM;
> > > > + break;
> > > > + }
> > > > +
> > > > + /*
> > > > + * Open every entry and get the file informations.
> > > > + *
> > > > + * Skip symbolic links during reading directory.
> > > > + */
> > > > + hDirEntry = CreateFile(full_dir_entry,
> > > > + GENERIC_READ,
> > > > + FILE_SHARE_READ | FILE_SHARE_WRITE
> > > > + | FILE_SHARE_DELETE,
> > > > + NULL,
> > > > + OPEN_EXISTING,
> > > > + FILE_FLAG_BACKUP_SEMANTICS
> > > > + | FILE_FLAG_OPEN_REPARSE_POINT,
> > > > + NULL);
> > > > +
> > > > + if (hDirEntry != INVALID_HANDLE_VALUE) {
> > > > + if (GetFileInformationByHandle(hDirEntry,
> > > > + &FileInfo) == TRUE) {
> > > > + attribute = FileInfo.dwFileAttributes;
> > > > +
> > > > + /* only save validate entries */
> > > > + if ((attribute & FILE_ATTRIBUTE_REPARSE_POINT) == 0) {
> > > > + if (index >= list_count) {
> > > > + list_count = list_count + 16;
> > >
> > > Magic number 16 again.
> > >
> > > > + file_id_list = g_realloc(file_id_list,
> > > > + sizeof(uint64_t)
> > > > + * list_count);
> > >
> > > OK, so here we are finally at the point where you chose the overall
> > > behaviour for this that we discussed before.
> > >
> > > So you are constantly appending 16 entry chunks to the end of the
> > > array, periodically reallocate the entire array, and potentially end
> > > up with one giant dense array with *all* file IDs of the directory.
> > >
> > > That's not really what I had in mind, as it still has the potential
> > > to easily crash QEMU if there are large directories on host.
> > > Theoretically a Windows directory might then consume up to 16 GB of
> > > RAM for looking up only one single directory.
> > >
> > > So is this the implementation that you said was very slow, or did
> > > you test a different one? Remember, my orgiginal idea (as starting
> > > point for Windows) was to only cache *one* file ID (the last being
> > > looked up). That's it. Not a list of file IDs.
> >
> > If only cache one file ID, that means for every read directory operation.
> > we need to look up whole directory to find out the next ID larger than last
> cached one.
> >
> > I provided some performance test in last patch:
> > Run test for read directory with 100, 1000, 10000 entries #1, For file
> > name cache solution, the time cost is: 2, 9, 44 (in ms).
> > #2, For file id cache solution, the time cost: 3, 438, 4338 (in ms). This
> is current solution.
> > #3, for cache one id solution, I just tested it: 4, 4788, more than
> > one minutes (in ms)
> >
> > I think it is not a good idea to cache one file id, it would be very
> > bad performance
>
> Yes, the performce would be lousy, but at least we would have a basis that
> just works^TM. Correct behaviour always comes before performance. And from
> there you could add additional patches on top to address performance
> improvements. Because the point is: your implementation is also suboptimal,
> and more importantly: prone to crashes like we discussed before.
>
> Regarding performance: for instance you are re-allocating an entire dense
> buffer on every 16 new entries. That will slow down things extremely. Please
> use a container from glib, because these are handling resize operations more
> smoothly for you out of the box, i.e. typically by doubling the container
> capacity instead of re-allocating frequently with small chunks like you did.
>
> However I am still not convinced that allocating a huge dense buffer with
> *all* file IDs of a directory makes sense.
>
> On the long-term it would make sense to do it like other implementations:
> store a snapshot of the directory temporarily on disk. That way it would not
> matter how huge the directory is. But that's a complex implementation, so not
> something that I would do in this series already.
>
> On the short/mid term I think we could simply make a mix of your solution and
> the one-ID solution that I suggested: keeping a maximum of e.g. 1k file IDs
> in RAM. And once guest seeks past that boundary, loading the subsequent 1k
> entries, free-ing the previous 1k entries, and so on.
>
Please note that the performance data is tested in native OS, but not in QEMU.
It is even worse in QEMU.
I run Linux guest OS on Windows host, use "ls -l" command to list a directory
with about 100 entries.
"ls -l" command need about 0.5 second to display one directory entry.
Caching only one node (file id, or file name, or others) will make 9pfs not
usable: listing 100 directory entries need 50 seconds in guest OS.
> > >
> > > > + }
> > > > + file_id = (uint64_t)FileInfo.nFileIndexLow
> > > > + +
> > > > + (((uint64_t)FileInfo.nFileIndexHigh)
> > > > + << 32);
> > > > +
> > > > +
> > > > + file_id_list[index] = file_id;
> > > > +
> > > > + if (strcmp(dd_data.name, ".") == 0) {
> > > > + stream->dot_id = file_id_list[index];
> > > > + if (index != 0) {
> > > > + sort_first_two_entry = 1;
> > > > + }
> > > > + } else if (strcmp(dd_data.name, "..") == 0) {
> > > > + stream->dot_dot_id = file_id_list[index];
> > > > + if (index != 1) {
> > > > + sort_first_two_entry = 1;
> > > > + }
> > > > + }
> > > > + index++;
> > > > + }
> > > > + }
> > > > + CloseHandle(hDirEntry);
> > > > + }
> > > > + g_free(full_dir_entry);
> > > > + find_status = _findnext(dd_handle, &dd_data);
> > > > + } while (find_status == 0);
> > > > +
> > > > + if (errno == ENOENT) {
> > > > + /* No more matching files could be found, clean errno */
> > > > + errno = 0;
> > > > + } else {
> > > > + err = errno;
> > > > + goto out;
> > > > + }
> > > > +
> > > > + stream->total_entries = index;
> > > > + stream->file_id_list = file_id_list;
> > > > +
> > > > + if (sort_first_two_entry == 0) {
> > > > + /*
> > > > + * If the first two entry is "." and "..", then do not sort
> them.
> > > > + *
> > > > + * If the guest OS always considers first two entries are
> > > > + "." and
> > > "..",
> > > > + * sort the two entries may cause confused display in guest
> OS.
> > > > + */
> > > > + qsort(&file_id_list[2], index - 2, sizeof(file_id),
> > > file_id_compare);
> > > > + } else {
> > > > + qsort(&file_id_list[0], index, sizeof(file_id),
> file_id_compare);
> > > > + }
> > >
> > > Were there cases where you did not get "." and ".." ?
> >
> > NTFS always provides "." and "..".
> > I could add more checks here to fix this risk
>
> That's what I assumed. So you can probably just drop this code for
> simplicity.
>
> >
> > >
> > > > +
> > > > +out:
> > > > + if (err != 0) {
> > > > + errno = err;
> > > > + if (stream != NULL) {
> > > > + if (file_id_list != NULL) {
> > > > + g_free(file_id_list);
> > > > + }
> > > > + CloseHandle(hDir);
> > > > + g_free(stream);
> > > > + stream = NULL;
> > > > + }
> > > > + }
> > > > +
> > > > + if (dd_handle != -1) {
> > > > + _findclose(dd_handle);
> > > > + }
> > > > +
> > > > + return (DIR *)stream;
> > > > +}
> > > > +
> > > > +/*
> > > > + * closedir_win32 - close a directory
> > > > + *
> > > > + * This function closes directory and free all cached resources.
> > > > + */
> > > > +int closedir_win32(DIR *pDir)
> > > > +{
> > > > + struct dir_win32 *stream = (struct dir_win32 *)pDir;
> > > > +
> > > > + if (stream == NULL) {
> > > > + errno = EBADF;
> > > > + return -1;
> > > > + }
> > > > +
> > > > + /* free all resources */
> > > > + CloseHandle(stream->hDir);
> > > > +
> > > > + g_free(stream->file_id_list);
> > > > +
> > > > + g_free(stream);
> > > > +
> > > > + return 0;
> > > > +}
> > > > +
> > > > +/*
> > > > + * readdir_win32 - read a directory
> > > > + *
> > > > + * This function reads a directory entry from cached entry list.
> > > > + */
> > > > +struct dirent *readdir_win32(DIR *pDir) {
> > > > + struct dir_win32 *stream = (struct dir_win32 *)pDir;
> > > > +
> > > > + if (stream == NULL) {
> > > > + errno = EBADF;
> > > > + return NULL;
> > > > + }
> > > > +
> > > > +retry:
> > > > +
> > > > + if (stream->offset >= stream->total_entries) {
> > > > + /* reach to the end, return NULL without set errno */
> > > > + return NULL;
> > > > + }
> > > > +
> > > > + if (get_next_entry(stream) != 0) {
> > > > + stream->offset++;
> > > > + goto retry;
> > > > + }
> > > > +
> > > > + /* Windows does not provide inode number */
> > > > + stream->dd_dir.d_ino = 0;
> > > > + stream->dd_dir.d_reclen = 0;
> > > > + stream->dd_dir.d_namlen = strlen(stream->dd_dir.d_name);
> > > > +
> > > > + stream->offset++;
> > > > +
> > > > + return &stream->dd_dir;
> > > > +}
> > > > +
> > > > +/*
> > > > + * rewinddir_win32 - reset directory stream
> > > > + *
> > > > + * This function resets the position of the directory stream to
> > > > +the
> > > > + * beginning of the directory.
> > > > + */
> > > > +void rewinddir_win32(DIR *pDir)
> > > > +{
> > > > + struct dir_win32 *stream = (struct dir_win32 *)pDir;
> > > > +
> > > > + if (stream == NULL) {
> > > > + errno = EBADF;
> > > > + return;
> > > > + }
> > > > +
> > > > + stream->offset = 0;
> > > > +
> > > > + return;
> > > > +}
> > > > +
> > > > +/*
> > > > + * seekdir_win32 - set the position of the next readdir() call in
> > > > +the directory
> > > > + *
> > > > + * This function sets the position of the next readdir() call in
> > > > +the directory
> > > > + * from which the next readdir() call will start.
> > > > + */
> > > > +void seekdir_win32(DIR *pDir, long pos) {
> > > > + struct dir_win32 *stream = (struct dir_win32 *)pDir;
> > > > +
> > > > + if (stream == NULL) {
> > > > + errno = EBADF;
> > > > + return;
> > > > + }
> > > > +
> > > > + if (pos < -1) {
> > > > + errno = EINVAL;
> > > > + return;
> > > > + }
> > > > +
> > > > + if (pos == -1 || pos >= (long)stream->total_entries) {
> > > > + /* seek to the end */
> > > > + stream->offset = stream->total_entries;
> > > > + return;
> > > > + }
> > > > +
> > > > + if (pos - (long)stream->offset == 0) {
> > > > + /* no need to seek */
> > > > + return;
> > > > + }
> > > > +
> > > > + stream->offset = pos;
> > > > +
> > > > + return;
> > > > +}
> > > > +
> > > > +/*
> > > > + * telldir_win32 - return current location in directory
> > > > + *
> > > > + * This function returns current location in directory.
> > > > + */
> > > > +long telldir_win32(DIR *pDir)
> > > > +{
> > > > + struct dir_win32 *stream = (struct dir_win32 *)pDir;
> > > > +
> > > > + if (stream == NULL) {
> > > > + errno = EBADF;
> > > > + return -1;
> > > > + }
> > > > +
> > > > + if (stream->offset > stream->total_entries) {
> > > > + return -1;
> > > > + }
> > > > +
> > > > + return (long)stream->offset;
> > > > +}
> > > >
> > >
> >
> >
> >
>
>