data_read(9)

💖 data_read(9) — Kernel API Manual, but make it a group chat 💖

okay so bestie, welcome to data_read — the read function for the "data" sysfs attribute. yes, that one. she's a sysfs read callback and she's literally the main character of this page. come on, let's get into it ✨

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🌸 SYNOPSIS 🌸

like, the whole vibe in one block:

ssize_t data_read (struct file *file , struct kobject *kobj , const
struct bin_attribute *attr , char *buffer , loff_t off , size_t size );

bestie she returns an ssize_t. noted. moving on 💅

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🎀 ARGUMENTS 🎀

six params, six little besties, let's meet them:

• file — the open file pointer 🫶
• kobj — the kobject of the sclp_sd_file object, iykyk
• attr — the data attribute (she's a data attribute, that's the whole thing)
• buffer — the target buffer, aka where the good stuff goes 🍓
• off — the requested file offset, like where in the file we're peeking 👀
• size — the requested number of bytes, the how-much-are-we-reading number

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🦋 DESCRIPTION 🦋

so what she does: she takes the requested portion of the Store Data entity contents and stores it into the specified buffer. that's it. that's the function. she ate 💅

and the return value? on success she hands you back the number of bytes she stored, or 0 on EOF. yes queen, 0 means EOF, don't @ me 😭

ngl, this is the part where you actually remember the return semantics: bytes stored on success, 0 on EOF. write it on your hand if you have to.

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✨ SEE ALSO ✨

the whole friend group, no cap — they all live in the kernel file ./drivers/s390/char/sclp_sd.c:

• struct sclp_sd_data(9)
• struct sclp_sd_listener(9)
• struct sclp_sd_file(9)
• sclp_sd_listener_add(9)
• sclp_sd_listener_remove(9)
• sclp_sd_listener_init(9)
• sclp_sd_receiver(9)
• sclp_sd_sync(9)
• sclp_sd_store_data(9)
• sclp_sd_data_reset(9)
• sclp_sd_file_release(9)
• sclp_sd_file_update(9)
• sclp_sd_file_update_async(9)
• reload_store(9)
• sclp_sd_file_create(9)
• sclp_sd_init(9)

go read them all, they're iconic, periodt 👑

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🌈 the cute little sign-off 🌈

this page lives in ./drivers/s390/char, and it's dated October 2026. so she's from the future AND from the s390 char drivers folder. obsessed. bye bestie, go read some sysfs attributes 🧚💜