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This new function calculates a buffer size suitable for holding the intended 9p request or response. For rather small message types (which applies to almost all 9p message types actually) simply use hard coded values. For some variable-length and potentially large message types calculate a more precise value according to what data is actually transmitted to avoid unnecessarily huge buffers. So p9_msg_buf_size() divides the individual 9p message types into 3 message size categories: - dynamically calculated message size (i.e. potentially large) - 8k hard coded message size - 4k hard coded message size As for the latter two hard coded message types: for most 9p message types it is pretty obvious whether they would always fit into 4k or 8k. But for some of them it depends on the maximum directory entry name length allowed by OS and filesystem for determining into which of the two size categories they would fit into. Currently Linux supports directory entry names up to NAME_MAX (255), however when comparing the limitation of individual filesystems, ReiserFS theoretically supports up to slightly below 4k long names. So in order to make this code more future proof, and as revisiting it later on is a bit tedious and has the potential to miss out details, the decision [1] was made to take 4k as basis as for max. name length. Link: https://lkml.kernel.org/r/bd6be891cf67e867688e8c8796d06408bfafa0d9.1657920926.git.linux_oss@crudebyte.com Link: https://lore.kernel.org/all/5564296.oo812IJUPE@silver/ [1] Signed-off-by: Christian Schoenebeck <linux_oss@crudebyte.com> Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>
20 lines
755 B
C
20 lines
755 B
C
/* SPDX-License-Identifier: GPL-2.0-only */
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/*
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* 9P Protocol Support Code
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*
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* Copyright (C) 2008 by Eric Van Hensbergen <ericvh@gmail.com>
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*
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* Base on code from Anthony Liguori <aliguori@us.ibm.com>
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* Copyright (C) 2008 by IBM, Corp.
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*/
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size_t p9_msg_buf_size(struct p9_client *c, enum p9_msg_t type,
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const char *fmt, va_list ap);
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int p9pdu_vwritef(struct p9_fcall *pdu, int proto_version, const char *fmt,
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va_list ap);
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int p9pdu_readf(struct p9_fcall *pdu, int proto_version, const char *fmt, ...);
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int p9pdu_prepare(struct p9_fcall *pdu, int16_t tag, int8_t type);
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int p9pdu_finalize(struct p9_client *clnt, struct p9_fcall *pdu);
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void p9pdu_reset(struct p9_fcall *pdu);
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size_t pdu_read(struct p9_fcall *pdu, void *data, size_t size);
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