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Jingbo Xu
cba0be1bed
Add fuse_lowlevel_notify_prune() helper, which sends FUSE_NOTIFY_PRUNE notification to kernel indicating that the server side's inode caches with resources e.g. file handle could be cleaned up if the corresponding dentry/inode caches (with dangling references) at the kernel side could be pruned out. This is a best-effort operation as inodes with active references are skipped. Signed-off-by: Jingbo Xu <jefflexu@linux.alibaba.com>
39 lines
1.9 KiB
Plaintext
39 lines
1.9 KiB
Plaintext
During the life-cycle of a user-space filesystem the usual flow is:
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1. User-space application does a filesystem-related syscall
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2. Kernel VFS calls into the FUSE kernel driver
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3. FUSE kernel redirects request to the user-space filesystem
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4. User-space server replies to request
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5. FUSE returns reply to VFS
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6. User-space application gets reply from the kernel
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However, there are occasions where the filesystem needs to send notifications to
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the kernel that are not in reply to any particular request. If, for example,
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when a READ request of 4096 bytes results in the filesystem having more data
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available for the specific inode, it may be useful to provide this extra data to
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the kernel cache so that future read operations will be faster.
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FUSE provides mechanisms for a user-space server to send the kernel certain
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types of asynchronous notifications. Currently, these are the available
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notifications:
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|-------------+----------------------------------|
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| Operation | libfuse function |
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|-------------+----------------------------------|
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| POLL | fuse_lowlevel_notify_poll |
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| INVAL_INODE | fuse_lowlevel_notify_inval_inode |
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| ENTRY | fuse_lowlevel_notify_inval_entry |
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| STORE | fuse_lowlevel_notify_store |
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| RETRIEVE | fuse_lowlevel_notify_retrieve |
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| DELETE | fuse_lowlevel_notify_delete |
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| RESEND | - |
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| PRUNE | fuse_lowlevel_notify_prune |
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|-------------+----------------------------------|
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One important restriction is that these asynchronous operations SHALL NOT be
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performed while executing other FUSE requests. Doing so will likely result in
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deadlocking the user-space filesystem server. In the example above, if the
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server is replying to a READ request and has extra data to add to the kernel
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cache, it needs to reply to the READ request first, and, e.g., signal a
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different thread to do the STORE.
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