POSIX_FADVISE(3POSIX)

📦 version 2017a, in debian bookworm, debian trixie, ubuntu jammy, ubuntu noble, ubuntu resolute, ubuntu stonking

💖 POSIX_FADVISE 💖

okay bestie, welcome to the POSIX Programmer's Manual page for posix_fadvise — she's from the 3POSIX section and she's literally here to whisper sweet hints to your kernel. 🎀

🌸 PROLOG 🌸

This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ — so if you're on Linux, bestie, go consult the corresponding Linux manual page for the details of Linux behavior. Or... it might not be implemented on Linux at all. 🙈 Yeah. It's giving "read the fine print."

✨ NAME ✨

posix_fadvise — file advisory information (ADVANCED REALTIME)

🦋 SYNOPSIS 🦋

#include <fcntl.h>

int posix_fadvise(int fd, off_t offset, off_t len, int advice);

💅 DESCRIPTION 💅

So basically, posix_fadvise() shall advise the implementation on the expected behavior of the application with respect to the data in the file associated with the open file descriptor, fd, starting at offset and continuing for len bytes. It's not a command, bestie — it's a hint. You're manifesting. ✨

The specified range need not currently exist in the file. Iconic, honestly — you can be out here advising about bytes that don't even exist yet.

If len is zero, all data following offset is specified. Zero means "everything from here on out," which is lowkey a lot of responsibility.

The implementation may use this information to optimize handling of the specified data. The posix_fadvise() function shall have no effect on the semantics of other operations on the specified data, although it may affect the performance of other operations. So like — no promises about behavior changing, but the vibes? The vibes can absolutely change.

The advice to be applied to the data is specified by the advice parameter and may be one of the following values:

  • POSIX_FADV_NORMAL — Specifies that the application has no advice to give on its behavior with respect to the specified data. It is the default characteristic if no advice is given for an open file. It's the "no thoughts, head empty" option and honestly, valid. 🫶
  • POSIX_FADV_SEQUENTIAL — Specifies that the application expects to access the specified data sequentially from lower offsets to higher offsets. Just going down the list, one by one, no skipping. Main character reading her feed in order. 👑
  • POSIX_FADV_RANDOM — Specifies that the application expects to access the specified data in a random order. Chaos mode. Shuffle play. We love her for it. 🔥
  • POSIX_FADV_WILLNEED — Specifies that the application expects to access the specified data in the near future. It's giving "pre-gaming." You're telling the implementation to get ready because you're about to show up. ⭐
  • POSIX_FADV_DONTNEED — Specifies that the application expects that it will not access the specified data in the near future. Not me telling the system "we're not gonna need this" — respectfully, we're done here. 💀
  • POSIX_FADV_NOREUSE — Specifies that the application expects to access the specified data once and then not reuse it thereafter. One and done. A single-serve friendship. No cap. 🍓

These values are defined in <fcntl.h>. That's where they live, bestie. Don't go looking elsewhere.

🌈 RETURN VALUE 🌈

Upon successful completion, posix_fadvise() shall return zero. Otherwise, an error number shall be returned to indicate the error.

Heads up, this is the weird one: she does not return -1 and set errno like your typical fave. She hands you the error number directly. Different energy. Same drama. 😭

🎀 ERRORS 🎀

The posix_fadvise() function shall fail if:

  • EBADF — The fd argument is not a valid file descriptor. She doesn't recognize that file descriptor. Who is she. 🙈
  • EINVAL — The value of advice is invalid, or the value of len is less than zero. Bad advice, or negative length. Neither is slaying today.
  • ESPIPE — The fd argument is associated with a pipe or FIFO. You tried to advise a pipe. She said no. 🚫

The following sections are informative. (Meaning: cute context, not the law. iykyk.)

🧚 EXAMPLES 🧚

None.

Not a single one. The example section said "no thoughts." Respect her privacy. 💜

👑 APPLICATION USAGE 👑

The posix_fadvise() function is part of the Advisory Information option and need not be provided on all implementations. So check before you assume, bestie — not every system is gonna have her.

🦄 RATIONALE 🦄

None.

No rationale given. She just is. Main character energy doesn't need to explain itself. 💅

🌟 FUTURE DIRECTIONS 🌟

None.

The future is unclear but she's not going anywhere. Or she is. We don't know. None.

🔍 SEE ALSO 🔍

  • posix_madvise()
  • The Base Definitions volume of POSIX.1‐2017, <fcntl.h>

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group.

In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. (Translation: if they disagree, the original wins. Periodt.) The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

okay that's the whole page bestie, every last crumb 💖

and that's the tea, fr fr — this one's brought to you by IEEE/The Open Group, 2017, page POSIX_FADVISE(3POSIX). go forth and advise responsibly, queen 🎀✨

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