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fscrypt: document gfp_flags for bounce page allocation

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Document that fscrypt_encrypt_pagecache_blocks() allocates the bounce
page from a mempool, and document what this means for the @gfp_flags
argument.

Link: https://lore.kernel.org/r/20191231181026.47400-1-ebiggers@kernel.org
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
This commit is contained in:
Eric Biggers 2019-12-31 12:10:26 -06:00
parent 796f12d742
commit 2d8f7f119b
1 changed files with 6 additions and 1 deletions
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7
fs/crypto/crypto.c
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@ -138,7 +138,7 @@ int fscrypt_crypt_block(const struct inode *inode, fscrypt_direction_t rw,
* multiple of the filesystem's block size.
* @offs: Byte offset within @page of the first block to encrypt. Must be
* a multiple of the filesystem's block size.
* @gfp_flags: Memory allocation flags
* @gfp_flags: Memory allocation flags. See details below.
*
* A new bounce page is allocated, and the specified block(s) are encrypted into
* it. In the bounce page, the ciphertext block(s) will be located at the same
@ -148,6 +148,11 @@ int fscrypt_crypt_block(const struct inode *inode, fscrypt_direction_t rw,
*
* This is for use by the filesystem's ->writepages() method.
*
* The bounce page allocation is mempool-backed, so it will always succeed when
* @gfp_flags includes __GFP_DIRECT_RECLAIM, e.g. when it's GFP_NOFS. However,
* only the first page of each bio can be allocated this way. To prevent
* deadlocks, for any additional pages a mask like GFP_NOWAIT must be used.
*
* Return: the new encrypted bounce page on success; an ERR_PTR() on failure
*/
struct page *fscrypt_encrypt_pagecache_blocks(struct page *page,