Difference between revisions of "UNIX Extensions"
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Some operating define additional classes of extended attribute (name/value pairs) which may be associated with an inode, and are available to be set by administrative users. Such classes of extended attributes include the "trusted" and "security" namespaces.
Revision as of 02:39, 10 March 2007
- 1 Introduction
- 2 Negotiating per-share (tree connection) Capabilities
- 3 New File Info (and Path Info) levels
- 4 New Query/Set FS Info levels: Operations on shares/exports
- 5 DFS Side Effects
The Unix Extensions to the CIFS Protocol have been done in stages. An initial set which included various new infolevels to TRANSACT2 commands in the range from 0x200 to 0x2FF (inclusive), was available when:
was included in the SMB negotiate protocol response.
Additional POSIX extensions have been added based on negotiating individual capabilities on the tree connection (via a Unix QueryFSInfo and SetFSInfo level). Following is a list of the capabilties which may be negotiated:
|CIFS_UNIX_POSIX_PATHNAMES_CAP||0x10 All characters except '/' should be supported in pathnames|
New File Info (and Path Info) levels
|QUERY_FILE_UNIX_BASIC||0x200||Part of the initial Unix Extensions|
|QUERY_FILE_UNIX_LINK||0x201||Part of the initial Unix Extensions|
|QUERY_POSIX_ACL||0x204||Requires CIFS_UNIX_POSIX_ACL_CAP, MUST be supported if set|
|QUERY_XATTR||0x205||Requires CIFS_UNIX_XATTR_CAP, MUST be supported if set|
|QUERY_ATTR_FLAGS||0x206||Requires CIFS_UNIX_EXTATTR_CAP, MUST be supported if set|
|QUERY_POSIX_LOCK||0x208||Requires CIFS_UNIX_FCNTL_CAP, MUST be supported if set|
|SMB_POSIX_PATH_OPEN||0x209||Requires CIFS_UNIX_POSIX_PATH_OPERATIONS_CAP, MUST be supported if set|
|SMB_POSIX_PATH_UNLINK||0x20a||Requires CIFS_UNIX_POSIX_PATH_OPERATIONS_CAP, SHOULD be supported if set|
|SMB_QUERY_FILE_UNIX_INFO2||0x20b||Requires CIFS_UNIX_EXTATTR_CAP, SHOULD be supported if set|
The server specifies it can serve these by returning CIFS_UNIX_POSIX_PATH_OPERATIONS_CAP in the reply to a trans2 qfsinfo (TRANSACT2_QFSINFO 0x03) info level SMB_QUERY_CIFS_UNIX_INFO (0x200) call. All values are little endian.
For open, call TRANSACT2_SETPATHINFO (command 0x06) info level :
The request data block should be 14 bytes consisting of the following :
|4 bytes||0||Flags field (same as smb_ntcreate_flags in SMBNTCreateX to request oplocks)|
|4 bytes||4||POSIX open flags (see below)|
|8 bytes||8||POSIX Permissions (see below)|
|2 bytes||16||Reply info level requested (see below)|
Encodings are as follows :
|POSIX open flags||Value|
|SMB_PERM_SUID||0004000||set UID bit|
|SMB_PERM_RUSR||00400||owner has read permission|
|SMB_PERM_WUSR||00200||owner has write permission|
|SMB_PERM_XUSR||00100||owner has execute permission|
|SMB_PERM_RGRP||00040||group has read permission|
|SMB_PERM_WGRP||00020||group has write permission|
|SMB_PERM_XGRP||00010||group has execute permission|
|SMB_PERM_ROTH||00004||others have read permission|
|SMB_PERM_WOTH||00002||others have write permission|
|SMB_PERM_XOTH||00001||others have execute permission|
Posix and Windows semantics for unlink of open files are different. POSIX allows deleting open files (which has the effect of removing them from the directory listing, preventing them from being opened again, but allowing existing users who have the file open to continue to read and write from the existing handle(s) until the handle(s) are closed when the inode or equivalent is deleted from the server).
The UNIX_INFO2 is an extension to the UNIX_BASIC info level. This info level can be used in FindFirst/FindNext, QueryPathInfo, QueryFileInfo and PosixOpen (but is not restricted to those calls).
The response block for the UNIX_INFO2 level is below. This is deliberately defined to be the same as UNIX_BASIC except for the last 3 fields.
|8||8||LARGE_INTEGER||Blocks||Number of blocks used on disk|
|8||16||LARGE_INTEGER||ChangeTime||Attribute change time|
|8||24||LARGE_INTEGER||LastAccessTime||Last access time|
|8||32||LARGE_INTEGER||LastModificationTime||Last modification time|
|8||40||LARGE_INTEGER||Uid||Numeric user id for the owner|
|8||48||LARGE_INTEGER||Gid||Numeric group id of owner|
|4||56||ULONG||Type||Enumeration specifying the file type|
|8||60||LARGE_INTEGER||DevMajor||Major device number if type is device|
|8||68||LARGE_INTEGER||DevMinor||Minor device number if type is device|
|8||76||LARGE_INTEGER||UniqueId||This is a server-assigned unique id|
|8||84||LARGE_INTEGER||Permissions||Standard UNIX permissions|
|8||92||LARGE_INTEGER||NumLinks||Number of hard links|
|4||108||ULONG||FileFlags||File flags enumeration|
|4||112||ULONG||FileFlagsMask||Mask of valid flags|
If the client is doing a set with the UNIX_INFO2 level and it does not want to alter the FileFlags, it should provide a FileFlagsMask of 0.
The defined set of file flags is
|EXT_SECURE_DELETE||0x00000001||File should be erased such that the data is not recoverable|
|EXT_ENABLE_UNDELETE||0x00000002||File should opt-in to a server-specific deletion recovery scheme|
|EXT_SYNCHRONOUS||0x00000004||I/O to this file should be performed synchronously|
|EXT_IMMUTABLE||0x00000008||NO changes can be made to this file|
|EXT_OPEN_APPEND_ONLY||0x00000010||Only appends can be made to this file|
|EXT_DO_NOT_BACKUP||0x00000020||Backup programs should ignore this file|
|EXT_NO_UPDATE_ATIME||0x00000040||The server is not required to update the last access time on this file|
|EXT_HIDDEN||0x00000080||User interface programs may ignore this file|
Described in the SNIA CIFS Technical Reference.
Described in the SNIA CIFS Technical Reference.
For setting file attribute flags (see man page for lsattr/chflags and equivalent)
__le64 mask; /* list of all possible attribute bits */ __le64 mode; /* list of actual attribute bits on this inode */ FILE_CHATTR_INFO /* ext attributes (chattr, chflags) level 0x206 */
xattrs (extended attributes) are of the form
namespace.key = value
Current xattrs in the "user" (also known as "OS2") namespace can readily map to SMB/CIFS EAs by simply stripping off the "user." in the namespace (prefix) sending only the key and value.
Some operating systems define additional classes of extended attribute (name/value pairs) which may be associated with an inode, and are available to be set by administrative users. Such classes of extended attributes include the "trusted" and "security" namespaces.
/* Do we need another field for flags? */ __u32 xattr_name_len; __u32 xattr_value_len; char xattr_name; /* followed by xattr_value[xattr_value_len], no pad */
FILE_XATTR_INFO /* extended attribute, info level 0x205 */
Sending attributes in the other namespace categories requires this new trans2 info level.
Note that the server may associate different default ACL permissions on xattrs in different namespaces on the same inode.
|Info Level Name||Value||Description|
|SMB_QUERY_CIFS_UNIX_INFO||0x200||(Part of the original Unix Extensions)|
The SMBWhoami extension is intended to be a lightweight method for a Unix client to be able to display sensible file ownership information.
SMBWhoami is performed by requesting a TRANS2_QFSINFO with an info level of SMB_QUERY_POSIX_WHOAMI. There are no parameters passed. The vuid (and optionally the tid) field is implicitly used.
|Info Level Name||Value|
The first two fields of the SMBWhoami response are a set of flags that further describe how the server has mapped the connected user. The mask is returned so that the client can distinguish which flag bits are meaningful.
|SMB_WHOAMI_GUEST||0x1||Logged in as (or squashed to) guest|
|4 bytes||0||Mapping flags|
|4 bytes||4||Mask of valid mapping flags|
|8 bytes||8||Primary user ID|
|8 bytes||16||Primary group ID|
|4 bytes||24||number of supplementary GIDs|
|4 bytes||28||number of SIDs|
|4 bytes||32||SID list byte count|
|4 bytes||36||Reserved (should be zero)|
|variable||...||list of 8 byte group IDs (may be empty)|
|variable||...||List of DOM_SID structures (may be empty)|
Note that the list of group IDs and DOM_SIDs are both optional. A server may choose not to return these (eg. if the information is expensive to gather). If these are not returned the corresponding count fields must be zero.
DFS Side Effects
The use of reserved path characters such as backslash, colon, asterik in DFS referrals can create interoperability problems. Many common clients and servers do not permit such characters in file or directory names. In particular many servers do not support either '\' or '/' in path components.
Although the CIFS_UNIX_POSIX_PATHNAMES_CAP implied the ability to recognize the backslash ('\') as a valid character in a directory or file name (rather than treating backslash as a path component separator) it was not required, and some common servers also can not handle the backslash within directory names in the response processing for DFS requests (in particular for TRANS2_GET_DFS_REFERRAL, trans2 command 0x10). DFS referrals requests and responses include a pathname which may include multiple levels of subdirectories. When CIFS_UNIX_POSIX_PATHNAMES_CAP is negotiated the server MAY report DFS paths which point to certain target storage servers (those which are known to support CIFS_UNIX_POSIX_PATHNANMES_CAP) as:
If the target storage server type is not known the server MAY canonicalize paths (replacing / with \) and report DFS paths as:
since / is not a valid path separator on some target servers. The client can detect that the server has canonicalized paths because the character that immediately follows the share is a '\' rather than a '/' character. Note that share names MUST not contain either the '\' or '/' character.
Paths which contain components with embedded backslash are expected to be rare in practice.