Extended Attributes API Specification (Rev #1)
ExtdAttrib
Introduction
ExtdAttrib distributes queries and changes on attributes. RISC OS standard file attributes are handled internally.
Each module which wants to provide additional attributes must register itself to this module. If a programm requests attributes for a given file ExtdAttrib passes this attributes to the according module. These will fill the required attribute information into a attribute result list if they can. The information can be passed onwards to further modules if required.
The space of memory for the attribute result list is provided by the calling application. The calling application can determine if its request shall be fulfilled directly or in a multitasking way if possible. At the latter the caller will obtain a query handle which can be requeried again and again until all attributes have been evaluated. The required size of the memory can be determined also. Because space of result belongs to the caller which might be swapped out during determining the attributes the values have to be cached locally until the module which provides the information is polled again by ExtdAttrib.
The calling application has also to pass on a list of attributes which it wants to obtain for a given file. Attributes distinguished by tags. The attributes are obtained in the same order is given inside the list which allows the calling program to fetch attributes which can be obtained without delay first and fetch attributes at the end whilst improving the obtained information continuously.
Attributes may be modificable and so ExtdAttrib provides a SWI with which an application can change modificable attributes of a given file. Even this operation can be performed in a multitasking way if desired.
What can you do with extended attributes?
The module overcomes some limitations of the OS. E.g. there are filing systems inside a multiuser network environment which are providing additional information about users which created or modified the files. The calling application (which is in general the filer) can evaluate this information on demand. Of course it must be prepared that not all attributes are available for all files.
<pBecause ExtdAttrib a and arbitrary attributes easy graphics handling implement including is it of provides sound thumbnail to viewer with>Note this all this is not provided ExtdAttrib itself but may be provided by additional modules or calling programs.
Displaying attributes
Your application has to enumerate the available attributes first. According the reported attribute tags it has to decided whether to handle the attribute or not. If it wants to handle an attribute it should put it into a list of required attributes. These list of attributes must be fetched for every file for which your application wants to report the attributes. This is done by calling the SWIs ExtdAttrib 0-7. This operation might be performed in a multitasking way if your application and the according attribut handlers are performing this. If the result of this query informs your application that an attirbute is writable for the given file your application may provide a possibility to change the value of the attribute. The change itself should be performed by the application by calling on of the SWIs ExtdAttrib 16-23.
Attributes
There is a descriptor for each attribute. It contains information about the type of the attribute, which determines how information is stored inside the query results and also provides some flags which tells you how an attribute is handled. Such a descriptor has the following format:
| Byte Offset | Meaning | |||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 0 | Size of entry including the size information. The size of the optional data can be calculated from this value. If 0 then tag is invalid. |
|||||||||||||||||||||||||||||||||||
| 4 | Attribute tag | |||||||||||||||||||||||||||||||||||
| 8 | Type of attribute
|
|||||||||||||||||||||||||||||||||||
| 12 | Attribute flags
|
|||||||||||||||||||||||||||||||||||
| 16 | Begin of optional attirbute specific data |
You can obtain a certain attribute descriptor by calling the SWI ExtdAttrib 9. The same SWI is used to enumerate the available attributes.
The following attribute tags have been specified in the moment. All other values are preserved.
| Group | Attribute tag | Name | Attribute type | Remarks |
|---|---|---|---|---|
| RISC OS | &00000000 - &0000001F | file attributes | 0 | |
| &00000020 | Load Address | 1 | ||
| &00000021 | Execution Address | 1 | ||
| &00000022 | File type | 1 | ||
| &00000023 | Update time | 3 | ||
| &00000024 | File size | 2 | ||
| &00000025 | File size on disc | 2 | ||
| &00000026 | Icon big | 7 | ||
| &00000027 | Icon small | 7 | ||
| Names | &00000100 | File path | 4 | |
| &00000101 | File name | 4 | ||
| Extended times | &00000111 | Creation time | 3 | |
| &00000112 | Time of last access | 3 | ||
| User information | &00000120 | Creation user | 4 | |
| &00000121 | Update user | 4 | ||
| &00000122 | User of last access | 4 | ||
| Misc Type info | &00000150 | File is for internal handling | 0 | To allow suppression of display of files used and maintained internally by the system |
| Special indication | &00000180 | Name of sound indicating file type | 4 | |
| Description | &00000200 | File short description | 4 | |
| &00000201 | File search keywords | 4 | ||
| Music | &00000300 | Title | 4 | |
| &00000301 | Interpret | 4 | ||
| &00000302 | Author | 4 | ||
| &00000303 | Verlag | 4 | ||
| &00000304 | Duration | 3 | ||
| &00000305 | Date of publishing | 3 | ||
| &00000310 | Type of Music | 1 | ||
| &00000320 | User dependent rating | 1 | ||
| &00000321 | Play volume | 1 | ||
| Revision Handling | &00000400 | Checkout state | 1 | |
| &00000410 | Checkout overlay small | 7 | ||
| &00000411 | Checkout overlay big | 7 | ||
| Graphics | &00000500 | Icon flexible | 7 | Required size has to be set by caller |
| Internal usage | &FFFFFFFF | Indicates start/end of list |
How to handle attributes
If you want to write an attribute handler please note the following considerations. An attribute may be fetched and maintained by several handlers. This can make sense e.g. think of a handler which keeps music titles inside a separate DB but a title can be also optionally stored inside inside the music file itself at certain music file formats. However it is likely that there are restrictions on the title length on both handlers. So it makes sense to pass on a fetch to both handlers and to store the longest information in the result. if changing an attribute it makes sense to pass the change to both handlers so that each handler can store the information as good as it can.
A handler must be able to fetch or modify an attribute in a non multitasking way. It may offer the possibilty to fetch/modify an attribute in a multitasking way. This concept has been choosen to ensure that program can operate in a non multitasking way.
...
Please contact ... to obtain additional tags.
Interfaces
ExtdAttrib_FetchAttribute
Fetches an attribute for a certain file.
On entry
R0 = Pointer to pollword (can be also used as identfier for the query).
R1 = Pointer to canonical file name.
R2 = Attribute tag.
R3 = Pointer to required attribute entry to obtain special request data.
R4 = Pointer to result entry for modification. May be 0 if only the required size has to be determined.
R5 = Pointer to data. This may be either free memory or the actual result. It can be 0 if there is no further memory or R4 is also 0 to obtain maximal amount of memory.
R6 = Maximal size of free memory or the actual result. The latter depends whater result is located immediately before free memory (purged flag set) or not. In first case it includes the free memory whilst in latter case it covers only the actually used memory. If R5 0 is 0 this value will be be also 0.
R7 = Information flags.Bit Meaning 0 1 indicates a new query, else it is a retry. 1 1 indicates that memory is purged which means that the result data is located in front of the free memory. 2 1 indicates that the fetch shall be done in multitaking mode if possible.
On exit
R0 = Result of fetch
Value Meaning <0 Error code which occurred inside the handler and should be passed on to ExtAttrib and the client. 0 Noted for multitasking but not fulfilled yet. Try later again. 1 Result modified. Pass on. 2 Result modified. Don't pass on. 3 Result not modified. Pass on. 4 Result not modified. Don't pass on. 5 Want to modify. Purge up and retry. R7 = If result is 1 or 2 this must contain the amount of modified additional memory data.
Use
-
A handler examines whether it can deliver or update an attribute result for the given file. If the fetch can be done in multitasking way it must note pointer to pollword and the pointer to the canonical file name. It can rely on these pointers and their content until a query is finished or aborted. It can't rely on the other pointers, so it may have to note the attribute specific data of the required attribute entry internally. Of course it must queue the request internally. After doing so it has to return a code of 0 in R0.
After a result has been determined inside a mulitasking way it must be buffered until the handler is requested again. The handler must not write the result into the result entry or the result data memory whilst it is not requested for there may be parallel activities. After the handler has determined the result it has to set pollword to non zero. Therefore it should disable the interrupts, write the pollword word and reenable the interrupts. The pollword needs not to be set when the handler is in ExtdAttrib_FetchAttribute for the attribute.
If a handler can't find a result e.g. for the required attribute doesn't exists for the given file it shall leave everything unchanged and return a code 3 or 4 in R0. It shall also return code 3 or 4 in case that there is already a result but the handler doesn't want to modify it.
If a handler wants to modify the result of an attribute its behaviour depends on the kind of attribute and thereon whether there is already a result or not. In most cases it will be enough to set the values from offset 4 of the result entry onwards. Note that the handler has always (even for strings) has to return the exact size of required data memory in R7 in case where offset 8 contains a offset to additional data. At strings this must include the terminator. At the flags the must not change Bits 0 and 1 which are mantained by ExtdAttrib. After performing the update the handler must return a code of 1 or 2 in R0. In case that the pointer to the result entry is 0 the handler can't evaluate any existing result and can't write its own result. It simply has to pass back the required amount of memory in R7 to allow determination of result memory.
If an attribute makes usage of additional result data this data has to be placed at that location which is given by R5. The length must no exceed the value given in R6 and may be limited by additonal information as told inside required attribute entry. Such a limitation has to be indicated by setting Bit 3 inside the flags of result entry. If the actual size is not big enough ExtdAttrib can be advised to rearrange the data in such a way that the additional result data for then actual attribute is located at the end of used memory. If this is the case or not will be indicated by the purged flag. If purged flag is 0 and more memory is required the handler can return a code of 4 to request a memory rearrangement after which ExtdAttrib will call the handler again with the purged flag set. The old entry can be overwritten and the additionally availlable memory can be used also. If there is still is not enough memory the handler shall use as much memory as available and makes sense (e.g. a string can be shortened but an icon of a specifc size can't) and set Bit 4 inside the flags of result entry.
ExtdAttrib_Abort
Aborts a pending operation.
On entry
R0 = Pointer to pollword indicating the operation to abort.
R1 = Reason information. If 1 then pending modifiactions should be made.
On exit
Nothing returned.
Use
-
The handler removes any internal things related to a pending fetch or modification. The pending activity is identified by the pointer to pollword.
This call may be done as a result of a SWI ExtdAttrib 9 call. However it may be caused also by a RMKill of ExtdAttrib and it may occur in case of optimized modifications to force the handler to perform the delayed modifications.
ExtdAttrib_ModifyAttribute
Modifies an attribute for a certain file.
On entry
R0 = Pointer to pollword (can be also used as identfier for the query).
R1 = Pointer to canonical file name.
R2 = Attribute tag.
R3 = Pointer to modify attribute entry containing the modification data.
R7 = Information flags.Bit Meaning 0 1 indicates a new query, else it is a retry. 1 Reserved 2 1 indicates that the fetch shall be done in multitaking mode if possible.
On exit
R0 = Result of fetch
Value Meaning <0 Error code which occurred inside the handler and should be passed on to ExtAttrib and the client. 0 Noted for multitasking but not fulfilled yet. Try later again. 1 Modified. Pass on. 2 Modified. Don't pass on. 3 Not modified. Pass on. 4 Not modified. Don't pass on. 5 Modified in an optimized way. Pass on. This sets a marker inside ExtdAttrib that something is still open for this modification on this handler and it must be called at the end of modification by ExtdAttrib_Abort. 6 Modified in an optimized way. Don't pass on.This sets a marker inside ExtdAttrib that something is still open for this modification on this handler and it must be called at the end of modification by ExtdAttrib_Abort.
Use
-
A handler examines whether it can modify an attribute result for the given file. If the modification can be done in multitasking way it must note pointer to pollword and the pointer to the canonical file name. It can rely on these pointers and their content until a query is finished or aborted. It can't rely on the other pointers, so ithave to note the modification data of the required attribute entry internally. Of course it must queue the request internally. After doing so it has to return a code of 0 in R0.
After a modifcation has been perfomed inside a mulitasking way the result must be noted until the handler is requested again. After the handler has performed the modification it has to set pollword to non zero. Therefore it should disable the interrupts, write the pollword word and reenable the interrupts. The pollword needs not to be set when the handler is in ExtdAttrib_ModifyAttribute for the attribute.
If a handler can't perfom the modifiaction a.g. for the required attribute doesn't exists for the given file it shall return a code 3 or 4 in R0. In case that a handler performed the update it shall return a code 1 or 2 in R0.
A handler can collect a couple of modifications e.g. for the RISC OS standard attributes and modify them in one go at the end. However the handler doesn't know when the last attribute chnage call happens. This may rely on the pass-on information of the other handlers too. Therefore it returns code 5 or 6 so that ExtAttrib knows that something must be done at the end and informs the handler by calling ExtdAttrib_Abort.
Service Calls
Service_DeclareAttribHandlers
(Service Call &)
On entry
On exit
Interrupt
Processor mode
Re-entrancy
Use
You must not claim this service call.
SWI Calls
ExtdAttrib
(SWI &)
Performs various actions to obtain and manipulate file attributes.
On entry
R0 = reason code
Other registers depend on reason code
On exit
R0 preserved
Other registers depend on reason code
Interrupt
Interrupts are enabled.
Fast Interrupts are enabled
Processor mode
Processor is in SVC mode
Re-entrancy
SWI is reentrant
Use
-
The particular action of ExtdAttrib is given by the reason code in R0 as follows:
R0 Action Page 0 Fetches file attributes using File$Path non multitasking. SWI ExtdAttrib 0-7 1 Fetches file attributes using a separate path string non multitasking. SWI ExtdAttrib 0-7 2 Fetches file attributes using a path variable non multitasking. SWI ExtdAttrib 0-7 3 Fetches file attributes non multitasking. SWI ExtdAttrib 0-7 4 Fetches file attributes using File$Path multitasking. SWI ExtdAttrib 0-7 5 Fetches file attributes using a separate path string multitasking. SWI ExtdAttrib 0-7 6 Fetches file attributes using a path variable multitasking. SWI ExtdAttrib 0-7 7 Fetches file attributes multitasking. SWI ExtdAttrib 0-7 8 Aborts a pending opreation in multitasking mode. SWI ExtdAttrib 8 9 Fetches information about a tag and enumerates the tags. SWI ExtdAttrib 9 10 Registers an attribute handler. SWI ExtdAttrib 10 11 Deregisters an attribute handler. SWI ExtdAttrib 11 16 Modifies file attributes using File$Path non multitasking. SWI ExtdAttrib 16-23 17 Modifies file attributes using a separate path string non multitasking. SWI ExtdAttrib 16-23 18 Modifies file attributes using a path variable non multitasking. SWI ExtdAttrib 16-23 19 Modifies file attributes non multitasking. SWI ExtdAttrib 16-23 20 Modifies file attributes using File$Path multitasking. SWI ExtdAttrib 16-23 21 Modifies file attributes using a separate path string multitasking. SWI ExtdAttrib 16-23 22 Modifies file attributes using a path variable multitasking. SWI ExtdAttrib 16-23 23 Modifies file attributes multitasking. SWI ExtdAttrib 16-23
ExtdAttrib 0-7
(SWI &)
Fetches file attributes
On entry
R0 = 0 to 7
R1 = pointer to object name
R2 = optional pointer to path string or path variable
R3 = Pointer to attribute result memory block. If set to 0 the maximal required size will be reported without generating the information.
R4 = Maximal size of attribute result memory block
R5 = Pointer to list with required attributes
R6 = Assigned query handle, must be 0 at start of a query.
On exit
R0-R3, R5 preserved
R4 = size of used block when all attributes collected, else preserved.
R6 = 0 when all attributes collected else assigned query handle.
R7 = Pollword for query if query not finished yet. Is kept during a query.
Use
-
The operation code determines the kind of file path handling
Bit 1 Bit 0 Path used 0 0 File$Path system variable 0 1 path string pointed to by R2 1 0 path variable pointed to by R2 1 1 none and the multitasking:
Bit 2 Multitasking mode 0 Single Task 1 Multitask If SWI is multitasking it returns the query handle and an automatically allocated pollword in case that a part of the query is processed in multitasking mode. In this case the according part is stored internally. You can either call the SWI periodically if you like or you can wait until pollword becomes non zero. However don´t make the assumption that if the pollword becomes non zero your query is entirely completed. It may only have become a bit more complete. So you may have to poll again and again.
The list containing the required attributes consists of one entry for each attributed with the following format:
Offset Meaning 0 Size of entry (incl. this size field) a size of zero marks end of list but without alignment. The size of the optional data can be calculated from this value.
The begin of the next entry must be word aligned.
4 Tag of the required attribute 8 Optional attribute specific data which format is determined by the attribute. The result consists of an array of entries which is preceded by the number of array elements and followed by detailed data for each attribute if the information doesn't fit into the array entry. The array will be set up at start completely. However the contents of the entries may change until the query is finished. To find out whether an entry is valid please check Bit 0 of the flags of an attribute.
Offset Meaning 0 Number of array elements. 4 Array of result entries. Each entry has the following format:
Offset Meaning 0 Attribute tag 4 Flags
Bit Meaning 0 Information is valid. May be invalid during queries in multitasking environments (Mantained by ExtdAttrib). 1 Attribute exists for the file (Mantained by ExtdAttrib). 2 Attribute is writable for the file 3 Data is incomplete due to limitation (only with attribute types 4 and 6). 4 Data is incomplete due to insufficient result memory. 8 32 Bit value or offset to data from start if available and required. 12 64 Bit value or size of data.
ExtdAttrib 8
(SWI &)
Aborts a pending operation in multitasking mode.
On entry
R0 = 8
R6 = handle of operation to abort.
On exit
All registers preserved
Use
Aborts the operation belonging to the given handle in multitasking mode. You must not perform any queries or modfications using this handle until it is passed again towards you as a result of new file attribute information fetch/modification.
ExtdAttrib 9
(SWI &)
Fetches information about a tag and enumerates the tags.
On entry
R0 = 9
R2 = Reserved. Must be set to 0.
R3 = Pointer to resulting attribute descriptor memory block. if set to 0 the maximal required size will be reported without generating the information.
R4 = Maximal size of tag result memory block.
R6 = Attribute tag for which information should be obtained. &FFFFFFFF indicates first tag in list.
On exit
R0-R3 preserved.
R6 = Number of next tag. &FFFFFFFF indicates end of tag list
Use
The request will return an attribute descriptor in the given memory which describes the given attribute. It also returns the attribute tag of the next attribute (in numerical ascending order) if available so that you can use this function to enumerate the attributes. However the information is retrieved directly from the registered attribute handlers. There can be several handlers registered for the same attribute. Only the information of the first handler will be returned. There might be slightly different internal flag information for each handler which must be therefore ignored by your evaluation.
ExtdAttrib 10
(SWI &)
Registers an attribute handler.
On entry
On exit
Use
ExtdAttrib 11
(SWI &)
Deregisters an attribute handler.
On entry
On exit
Use
ExtdAttrib 16-23
(SWI &)
Changes attributes for a given file.
On entry
R0 = 16 to 23
R1 = pointer to object name
R2 = optional pointer to path string or path variable
R5 = Pointer to list with modified attributes
R6 = Assigned query handle, must be 0 at start of a query.
On exit
R0-R2, R5 preserved
R6 = 0 when all attributes modified else assigned query handle.
R7 = Pollword for query if query not finished yet. Is kept during a query.
Use
-
The operation codes determine the kind of file path handling and the multitasking in the same kind as described under the fetching of attributes.
The list containing the modified attributes consists of one entry for each attributed with the following format:
Offset Meaning 0 Size of entry (incl. this size field) a size of zero marks end of list but without alignment. The size of the modified data can be calculated from this value.
The begin of the next entry must be word aligned.
4 Tag of the attribute which should be modified.
8 Number of modifications performed. Bit 31=1 indicates that modification is complete.
12 Modified attribute data which format is determined by the attribute.
The number of modifications is increased for every modification done by a handler. If used in multitasking mode the program can evaluate which attributes have been modified for the file.
</body> </html>Social
and
ROOL Store
Buy RISC OS Open merchandise here, including SD cards for Raspberry Pi and more.