Re: [Haskell-beginners] R/W from/to partitions (on linux)

also what happens to the result of Lazy.hGetContents after i close the handle i used for accessing the file content? can i still browse the part of th file cached? will there be an exception? it does not seem to be the case from tests on GHCI but then... 2017-06-26 10:35 GMT+02:00 Silent Leaf :

i'm reading on the doc of BS.Lazy.hGetContents: "Once EOF is encountered, the Handle is closed."

what does that imply if i'm using it inside of withFile? no risk of getting prematurely out of the function right? that doesn seem possible in a pure function but i'm asking either way. if say i do something that reads the whole file, say calculating its length, does it mean since EOF will be reached i'll have to open the file again? i think i'm a bit lost...

i'm trying to find how to read big chunks of two files, do stuff with each pair of chunk, and so on till the EOF, which may or may not happen at the same time for both... i don't really know how lazy bytestrings handle, for example, taking too much from a file. one way would be to calculate the length, ofc, but for files (partition) of several dozens of gigabytes, it's a bit delicate... the ideal would be to get the length from the system itself rather than calculate the whole string ...

2017-06-26 7:57 GMT+02:00 Silent Leaf :

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Darn quick answer! Thanks Sylvain, that may be all i need to start!

2017-06-26 7:51 GMT+02:00 Sylvain Henry :

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Hi,

It is not Haskell specific. You just have to read from the partition device special file (e.g., something like /dev/sdb2) as you would do with a normal file. You must have the permission to do so (e.g., be root). Be careful as you can destroy your system if you write something incorrect in your partitions.

Repositioning handles: https://www.stackage.org/haddo ck/lts-8.20/base-4.9.1.0/System-IO.html#g:13

Read/write: https://www.stackage.org/haddock/lts-8.20/base-4.9.1.0/Syste m-IO.html#v:hPutBuf

Sylvain

On 26/06/2017 07:35, Silent Leaf wrote:

Hi,

I'd like to be able to read and write from/to partitions directly. I've had trouble with the documentation (honestly i can't find anything, and any mention of partitions leads to mathematical partitioning of lists or whatever).

I obviously would need to be able to write or read from a specific position in the partition. Mind you that would be good too for files (that is, being able to read/write from a specific position in it) since i plan on making disk images.

Thanks in advance!

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