Orange Pi5 kernel

^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300   1) =========
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300   2) RPC Cache
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300   3) =========
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300   4) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300   5) This document gives a brief introduction to the caching
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300   6) mechanisms in the sunrpc layer that is used, in particular,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300   7) for NFS authentication.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300   8) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300   9) Caches
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  10) ======
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  11) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  12) The caching replaces the old exports table and allows for
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  13) a wide variety of values to be caches.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  14) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  15) There are a number of caches that are similar in structure though
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  16) quite possibly very different in content and use.  There is a corpus
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  17) of common code for managing these caches.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  18) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  19) Examples of caches that are likely to be needed are:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  20) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  21)   - mapping from IP address to client name
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  22)   - mapping from client name and filesystem to export options
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  23)   - mapping from UID to list of GIDs, to work around NFS's limitation
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  24)     of 16 gids.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  25)   - mappings between local UID/GID and remote UID/GID for sites that
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  26)     do not have uniform uid assignment
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  27)   - mapping from network identify to public key for crypto authentication.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  28) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  29) The common code handles such things as:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  30) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  31)    - general cache lookup with correct locking
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  32)    - supporting 'NEGATIVE' as well as positive entries
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  33)    - allowing an EXPIRED time on cache items, and removing
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  34)      items after they expire, and are no longer in-use.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  35)    - making requests to user-space to fill in cache entries
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  36)    - allowing user-space to directly set entries in the cache
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  37)    - delaying RPC requests that depend on as-yet incomplete
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  38)      cache entries, and replaying those requests when the cache entry
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  39)      is complete.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  40)    - clean out old entries as they expire.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  41) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  42) Creating a Cache
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  43) ----------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  44) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  45) -  A cache needs a datum to store.  This is in the form of a
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  46)    structure definition that must contain a struct cache_head
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  47)    as an element, usually the first.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  48)    It will also contain a key and some content.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  49)    Each cache element is reference counted and contains
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  50)    expiry and update times for use in cache management.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  51) -  A cache needs a "cache_detail" structure that
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  52)    describes the cache.  This stores the hash table, some
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  53)    parameters for cache management, and some operations detailing how
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  54)    to work with particular cache items.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  55) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  56)    The operations are:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  57) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  58)     struct cache_head \*alloc(void)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  59)       This simply allocates appropriate memory and returns
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  60)       a pointer to the cache_detail embedded within the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  61)       structure
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  62) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  63)     void cache_put(struct kref \*)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  64)       This is called when the last reference to an item is
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  65)       dropped.  The pointer passed is to the 'ref' field
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  66)       in the cache_head.  cache_put should release any
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  67)       references create by 'cache_init' and, if CACHE_VALID
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  68)       is set, any references created by cache_update.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  69)       It should then release the memory allocated by
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  70)       'alloc'.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  71) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  72)     int match(struct cache_head \*orig, struct cache_head \*new)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  73)       test if the keys in the two structures match.  Return
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  74)       1 if they do, 0 if they don't.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  75) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  76)     void init(struct cache_head \*orig, struct cache_head \*new)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  77)       Set the 'key' fields in 'new' from 'orig'.  This may
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  78)       include taking references to shared objects.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  79) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  80)     void update(struct cache_head \*orig, struct cache_head \*new)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  81)       Set the 'content' fileds in 'new' from 'orig'.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  82) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  83)     int cache_show(struct seq_file \*m, struct cache_detail \*cd, struct cache_head \*h)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  84)       Optional.  Used to provide a /proc file that lists the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  85)       contents of a cache.  This should show one item,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  86)       usually on just one line.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  87) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  88)     int cache_request(struct cache_detail \*cd, struct cache_head \*h, char \*\*bpp, int \*blen)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  89)       Format a request to be send to user-space for an item
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  90)       to be instantiated.  \*bpp is a buffer of size \*blen.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  91)       bpp should be moved forward over the encoded message,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  92)       and  \*blen should be reduced to show how much free
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  93)       space remains.  Return 0 on success or <0 if not
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  94)       enough room or other problem.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  95) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  96)     int cache_parse(struct cache_detail \*cd, char \*buf, int len)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  97)       A message from user space has arrived to fill out a
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  98)       cache entry.  It is in 'buf' of length 'len'.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  99)       cache_parse should parse this, find the item in the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 100)       cache with sunrpc_cache_lookup_rcu, and update the item
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 101)       with sunrpc_cache_update.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 102) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 103) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 104) -  A cache needs to be registered using cache_register().  This
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 105)    includes it on a list of caches that will be regularly
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 106)    cleaned to discard old data.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 107) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 108) Using a cache
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 109) -------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 110) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 111) To find a value in a cache, call sunrpc_cache_lookup_rcu passing a pointer
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 112) to the cache_head in a sample item with the 'key' fields filled in.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 113) This will be passed to ->match to identify the target entry.  If no
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 114) entry is found, a new entry will be create, added to the cache, and
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 115) marked as not containing valid data.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 116) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 117) The item returned is typically passed to cache_check which will check
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 118) if the data is valid, and may initiate an up-call to get fresh data.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 119) cache_check will return -ENOENT in the entry is negative or if an up
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 120) call is needed but not possible, -EAGAIN if an upcall is pending,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 121) or 0 if the data is valid;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 122) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 123) cache_check can be passed a "struct cache_req\*".  This structure is
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 124) typically embedded in the actual request and can be used to create a
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 125) deferred copy of the request (struct cache_deferred_req).  This is
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 126) done when the found cache item is not uptodate, but the is reason to
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 127) believe that userspace might provide information soon.  When the cache
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 128) item does become valid, the deferred copy of the request will be
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 129) revisited (->revisit).  It is expected that this method will
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 130) reschedule the request for processing.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 131) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 132) The value returned by sunrpc_cache_lookup_rcu can also be passed to
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 133) sunrpc_cache_update to set the content for the item.  A second item is
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 134) passed which should hold the content.  If the item found by _lookup
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 135) has valid data, then it is discarded and a new item is created.  This
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 136) saves any user of an item from worrying about content changing while
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 137) it is being inspected.  If the item found by _lookup does not contain
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 138) valid data, then the content is copied across and CACHE_VALID is set.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 139) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 140) Populating a cache
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 141) ------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 142) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 143) Each cache has a name, and when the cache is registered, a directory
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 144) with that name is created in /proc/net/rpc
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 145) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 146) This directory contains a file called 'channel' which is a channel
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 147) for communicating between kernel and user for populating the cache.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 148) This directory may later contain other files of interacting
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 149) with the cache.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 150) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 151) The 'channel' works a bit like a datagram socket. Each 'write' is
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 152) passed as a whole to the cache for parsing and interpretation.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 153) Each cache can treat the write requests differently, but it is
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 154) expected that a message written will contain:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 155) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 156)   - a key
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 157)   - an expiry time
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 158)   - a content.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 159) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 160) with the intention that an item in the cache with the give key
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 161) should be create or updated to have the given content, and the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 162) expiry time should be set on that item.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 163) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 164) Reading from a channel is a bit more interesting.  When a cache
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 165) lookup fails, or when it succeeds but finds an entry that may soon
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 166) expire, a request is lodged for that cache item to be updated by
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 167) user-space.  These requests appear in the channel file.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 168) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 169) Successive reads will return successive requests.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 170) If there are no more requests to return, read will return EOF, but a
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 171) select or poll for read will block waiting for another request to be
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 172) added.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 173) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 174) Thus a user-space helper is likely to::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 175) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 176)   open the channel.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 177)     select for readable
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 178)     read a request
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 179)     write a response
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 180)   loop.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 181) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 182) If it dies and needs to be restarted, any requests that have not been
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 183) answered will still appear in the file and will be read by the new
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 184) instance of the helper.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 185) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 186) Each cache should define a "cache_parse" method which takes a message
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 187) written from user-space and processes it.  It should return an error
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 188) (which propagates back to the write syscall) or 0.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 189) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 190) Each cache should also define a "cache_request" method which
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 191) takes a cache item and encodes a request into the buffer
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 192) provided.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 193) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 194) .. note::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 195)   If a cache has no active readers on the channel, and has had not
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 196)   active readers for more than 60 seconds, further requests will not be
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 197)   added to the channel but instead all lookups that do not find a valid
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 198)   entry will fail.  This is partly for backward compatibility: The
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 199)   previous nfs exports table was deemed to be authoritative and a
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 200)   failed lookup meant a definite 'no'.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 201) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 202) request/response format
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 203) -----------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 204) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 205) While each cache is free to use its own format for requests
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 206) and responses over channel, the following is recommended as
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 207) appropriate and support routines are available to help:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 208) Each request or response record should be printable ASCII
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 209) with precisely one newline character which should be at the end.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 210) Fields within the record should be separated by spaces, normally one.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 211) If spaces, newlines, or nul characters are needed in a field they
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 212) much be quoted.  two mechanisms are available:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 213) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 214) -  If a field begins '\x' then it must contain an even number of
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 215)    hex digits, and pairs of these digits provide the bytes in the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 216)    field.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 217) -  otherwise a \ in the field must be followed by 3 octal digits
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 218)    which give the code for a byte.  Other characters are treated
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 219)    as them selves.  At the very least, space, newline, nul, and
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 220)    '\' must be quoted in this way.